<PAGE>

                                                                     EXHIBIT 4.1

NEITHER THIS WARRANT NOR THE SHARES OF STOCK ISSUABLE UPON EXERCISE HEREOF HAVE
BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED. NO SALE, TRANSFER
OR OTHER DISPOSITION OF THIS WARRANT OR SAID SHARES MAY BE EFFECTED WITHOUT (I)
AN EFFECTIVE REGISTRATION STATEMENT RELATED THERETO, OR (II) AN OPINION OF
COUNSEL, REASONABLY SATISFACTORY TO COUNSEL TO THE COMPANY, THAT AN EXEMPTION
FROM REGISTRATION UNDER SAID ACT IS AVAILABLE.

December 31, 2002             AMENDED AND RESTATED                Warrant No.: 6
                             STOCK PURCHASE WARRANT

              To Subscribe for and Purchase Class A Common Stock of

                            NEXTERA ENTERPRISES, INC.

      THIS AMENDED AND RESTATED STOCK PURCHASE WARRANT ("Warrant") certifies
that, for value received, Fleet National Bank (together with any subsequent
transferees of all or any portion of this Warrant, the "Holder"), is entitled,
upon the terms and subject to the conditions hereinafter set forth, to subscribe
for and purchase from Nextera Enterprises, Inc., a Delaware corporation
(hereinafter called the "Company"), up to six hundred forty-four thousand, seven
hundred and four (644,704) fully paid and non-assessable shares of the Company's
Class A Common Stock, $0.001 par value per share (the "Shares"), at the price
equal to the Exercise Price (as defined in Section 1 hereof) (subject to
adjustment as provided in Section 7 hereof). The number and character of such
Shares are subject to adjustment as provided herein. Capitalized terms used
herein and not defined herein shall have the meanings given such terms in that
certain Second Amended and Restated Credit Agreement dated December 31, 2002, by
and among the Company, the Holder and the other lenders party thereto (the
"Credit Agreement"; and together with all related promissory notes, mortgages,
guaranties, agreements, documents and instruments from time to time entered into
by Company and any other person or obligor pursuant thereto, the "Credit
Documents").

      This Warrant amends and restates in its entirety that certain Warrant for
up to six hundred forty-four thousand, seven hundred and four (644,704) fully
paid and non-assessable shares of the Company's Class A Common Stock, $0.001 par
value per share dated on March 29, 2002 (the "Prior Warrant") made by the
Company in favor of the Holder.

      1.    Definitions. As used herein the following terms shall have the
            following meanings:


            "Act" means the Securities Act of 1933 as amended, or a similar
            Federal statute and the rules and regulations of the Commission
            issued under that Act, as they each may, from time to time, be in
            effect.

            "Additional Shares of Common Stock" shall mean all shares of Common
            Stock issued (or, pursuant to Section 7(c), deemed to be issued) by
            the Company after the Original Issue Date, but shall not include:

            (A) shares of Common Stock issued or issuable upon conversion of
            shares of all of preferred stock of the Company outstanding as of
            the Original Issue Date;

            (B) shares of Common Stock issued or issuable upon exercise of this
            Warrant or any other warrant or option of the Company outstanding as
            of the Original Issue Date;

            (C) shares of Common Stock issued by way of dividend or other
            distribution on shares of Common Stock excluded from the definition
            of Additional Shares of Common Stock by the foregoing clause (A) or
            (B) or on Common Stock so excluded; or
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            (D) shares issued under an employee stock purchase plan or pursuant
            to options exercisable for shares of Common Stock (such number
            subject to equitable adjustment in the event of any stock dividend,
            stock split, combination, reorganization, recapitalization,
            reclassification or other similar event), issued after the date of
            this Warrant to directors, officers, employees or consultants of the
            Company and any Subsidiary pursuant to any qualified or
            non-qualified stock option plan or other equity incentive plan
            approved by the Board of Directors of the Company, equal to the
            first 30% of the outstanding stock of the Company, calculated on a
            post-Original Issue Date, fully-diluted basis.

            "Common Stock" shall mean the Class A Common Stock of the Company,
            $0.001 par value per share.

            "Convertible Securities" shall mean any evidences of indebtedness,
            shares or other securities directly or indirectly convertible into
            or exchangeable for Common Stock.

            "Exercise Price" shall mean $0.86 per share.

            "New Financing Source" shall mean a source other than the Company.

            "Option" shall mean rights, options or warrants to subscribe for,
            purchase or otherwise acquire Common Stock or Convertible
            Securities.

            "Original Issue Date" shall mean the date on which this Warrant is
            originally issued.

      2. Purchase Rights. The purchase rights represented by this Warrant are
exercisable by the Holder in whole or in part (and not as to a fractional
share), at any time and from time to time commencing on the date hereof and
ending at 5:00 p.m. on the date (the "Expiration Date") eighteen (18) months
after the indefeasible payment in full in cash or cash equivalents of the Credit
Obligations.

      3. Exercise of Warrant; Net Issue Exercise.

      3.1 Exercise of Warrant. Subject to Section 2 above, the purchase rights
represented by this Warrant may be exercised, in whole or in part and from time
to time, by the surrender of this Warrant and the duly executed Notice of
Exercise (the form of which is attached as Exhibit A) at the principal office of
the Company and by the payment to the Company, by check, of an amount equal to
the then applicable Exercise Price per share multiplied by the number of Shares
then being purchased. Upon exercise, the Holder shall be entitled to receive,
within a reasonable time, a certificate or certificates, issued in the Holder's
name or in such name or names as the Holder may direct, for the number of Shares
so purchased. The Shares so purchased shall be deemed to be issued as of the
close of business on the date on which this Warrant shall have been exercised.

      3.2. Net Issue Exercise.

            (a) In lieu of exercising this Warrant as set forth in Section 3.1,
      the Holder may elect to receive Shares equal to the value of this Warrant
      (or the portion thereof being cancelled) by surrender of this Warrant at
      the principal office of the Company together with notice of such election
      in which event the Company shall issue to the Holder a number of Shares
      computed using the following formula:

                                  X = Y (A - B)
                                      ---------
                                          A

Where X = the number of Shares to be issued to the Holder;


                                       2
<PAGE>
      Y=    the number of Shares purchasable under this Warrant, or if only a
            portion of this Warrant is being cancelled, the gross number of
            Shares covered by the portion of this Warrant being cancelled;

      A=    the fair market value of one Share, as determined by the Board of
            Directors of the Company pursuant to paragraph (b) below, as at the
            time the net issue election is made pursuant to this Section (the
            "Determination Date"); and

      B=    the Exercise Price (as adjusted to the date of such calculations).

Such Shares shall be issued as soon as practicable after the Determination Date.

            (b) For purposes of this Section, fair market value of a Share shall
      be determined as follows:

                        (A) If the Company's Common Stock is not publicly traded
                  at the Determination Date, the fair market value of a Share
                  shall be a value reasonably determined by the Company's Board
                  of Directors. In the event that the Holder disagrees with the
                  Board of Directors' determination of fair market value, then
                  the fair market value shall be determined by an appraiser
                  selected by the Holder (the "Holder's Appraiser") and whose
                  appraisal (the "Holder's Appraisal") shall be furnished to the
                  Company within 20 days after the Board of Directors'
                  determination of fair value, and if the Company does not
                  object to such determination within 15 days after receipt of
                  the Holder's appraisal, then the fair market value determined
                  by the Holder's Appraiser shall be the fair market value of a
                  Share. In the event that the Company objects to such
                  determination then the Company shall select an appraiser (the
                  "Company's Appraiser") who shall review the determination of
                  the Holder's Appraiser and issue a report thereon (the
                  "Company's Appraisal") within 30 days after the delivery of
                  the Holder's Appraisal to the Company and within 10 days after
                  the issuance of such report to the Holder's Appraiser, the
                  Holder's Appraiser and the Company's Appraiser shall meet to
                  negotiate in good faith to reach agreement on the fair market
                  value of a Share, and such agreed value shall be the fair
                  market value of a Share. In the event that the Company's
                  Appraiser and the Holder's Appraiser are unable to reach
                  agreement then such Appraisers shall select an appraiser (the
                  "Third Appraiser") within 5 days after the meeting between the
                  Holder's Appraiser and the Company's Appraiser, and the
                  average of two appraisals, consisting of the appraisal made by
                  the Third Appraiser and the appraisal of the Holder's
                  Appraiser and Company's Appraiser (whichever is closest to
                  that of the Third Appraiser), shall be conclusive and binding
                  on the Company and the Holder. The Company and the Holder
                  shall each pay one half (1/2) of the fees and expenses of each
                  of the Company's Appraiser, the Holder's Appraiser and the
                  Third Appraiser.

                        (B) if the Company's Common Stock is publicly traded on
                  the Determination Date, the fair market value of a Share shall
                  be equal to (1) the average of the closing prices quoted on
                  the Nasdaq Stock Exchange, Inc., if applicable, or the average
                  of the last bid and asked prices of the Common Stock quoted in
                  the Nasdaq OTC Bulletin Board or the over-the-counter-market,
                  or (2) if the Common Stock is then traded on a national
                  securities exchange, the average of the high and low closing
                  prices of the Common Stock listed on the principal national
                  securities exchange on which the Common Stock is so traded, in
                  each case for the twenty (20) trading days preceding the
                  Determination Date.

      4. Shares to be Issued; Reservation of Shares. The Company covenants that
the Shares that may be issued upon the exercise of the purchase rights
represented by this Warrant will, upon issuance, be fully paid and
non-assessable, and free from all liens and charges with respect to the issue


                                       3
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thereof. During the period within which the purchase rights represented by the
Warrant may be exercised, the Company will at all times have authorized and
reserved, for the purpose of issuance upon exercise of the purchase rights
represented by this Warrant, a sufficient number of shares of its Common Stock
to provide for the exercise of the right represented by this Warrant.

      5. No Fractional Shares. No fractional shares shall be issued upon the
exercise of this Warrant. In lieu thereof, a cash payment shall be made equal to
such fraction multiplied by the fair market value of such shares of Common
Stock, as determined pursuant to Section 3.2(b) above.

      6. Adjustment for Merger, Consolidation or Sale of Assets. In the event
that at any time or from time to time after the Original Issue Date, the Company
shall merge or consolidate with or into another entity or sell all or
substantially all of its assets, the Holder hereof shall thereafter have the
right to receive the kind and amount of shares of stock, other securities,
property or cash deliverable or payable to the holders of the Common Stock of
the Company that the Holder hereof upon exercise of this Warrant would have been
entitled to had the Holder hereof exercised the remaining portion of this
Warrant into shares of Common Stock immediately prior thereto.

      7. Adjustment of Exercise Price and Number of Shares.

            (a) Adjustment of Exercise Price and Number of Shares. The Exercise
      Price and number of shares of Common Stock issuable upon the exercise of
      the Warrant shall be adjusted as set forth in this Section 7 with the
      intent that the rights of the Holder to exercise shall not be impaired.

            (b) Adjustment for Combination, Consolidation, Stock Dividend or
      Subdivision of Common Stock. If the outstanding shares of Common Stock
      shall be subdivided into a greater number of shares or a dividend in
      Common Stock shall be paid in respect of Common Stock, the Exercise Price
      in effect immediately prior to such subdivision or at the record date of
      such dividend shall simultaneously with the effectiveness of such
      subdivision or immediately after the record date of such dividend be
      proportionately reduced. If outstanding shares of Common Stock shall be
      combined or consolidated into a smaller number of shares, the Exercise
      Price in effect immediately prior to such combination or consolidation
      shall, simultaneously with the effectiveness of such combination or
      consolidation, be proportionately increased. When any adjustment is
      required to be made in the Exercise Price, the number of shares of Common
      Stock purchasable upon the exercise of this Warrant shall be changed to
      the number determined by dividing (i) an amount equal to the number of
      shares issuable upon the exercise of this Warrant immediately prior to
      such adjustment, multiplied by the Exercise Price in effect immediately
      prior to such adjustment, by (ii) the Exercise Price in effect immediately
      after such adjustment.

            (c) Issue of Options and Convertible Securities Deemed Issue of
      Additional Shares of Common Stock. If the Company at any time or from time
      to time after the Original Issue Date shall issue any Options or
      Convertible Securities or shall fix a record date for the determination of
      holders of any class of securities entitled to receive any such Options or
      Convertible Securities, then the maximum number of shares of Common Stock
      (as set forth in the instrument relating thereto, without regard to any
      provision contained therein for a subsequent adjustment of such number)
      issuable upon the exercise of such Options or, in the case of Convertible
      Securities or Options therefor, the conversion or exchange of such
      Convertible Securities, shall be deemed to be Additional Shares of Common
      Stock issued as of the time of such issue or, in case such a record date
      shall have been fixed, as of the close of business on such record date,
      provided that Additional Shares of Common Stock shall not be deemed to
      have been issued unless the consideration per share (determined pursuant
      to paragraph (e) below) of such Additional Shares of Common Stock would be
      less than the Exercise Price in effect on the date of and immediately
      prior to such issue, or such record date, as the case may be, and provided
      further in any such case in which Additional Shares of Common Stock are
      deemed to be issued:


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<PAGE>
                  (i) No further adjustment in the Exercise Price shall be made
            upon the subsequent issue of Convertible Securities or shares of
            Common Stock upon the exercise of such Options or conversion or
            exchange of such Convertible Securities;

                  (ii) If such Options or Convertible Securities by their terms
            provide, with the passage of time or otherwise, for any increase in
            the consideration payable to the Company, or decrease in the number
            of shares of Common Stock issuable, upon the exercise, conversion or
            exchange thereof, the Exercise Price computed upon the original
            issue thereof (or upon the occurrence of a record date with respect
            thereto), and any subsequent adjustments based thereon, shall, upon
            any such increase or decrease becoming effective, be recomputed to
            reflect such increase or decrease insofar as it affects such Options
            or the rights of conversion or exchange under such Convertible
            Securities;

                  (iii) No readjustment pursuant to clause (ii) above shall have
            the effect of increasing the Exercise Price to an amount which
            exceeds the lower of (A) the Exercise Price immediately prior to the
            adjustment affected upon the original issue of Options or
            Convertible Securities (or upon the occurrence of a record date with
            respect thereto) pursuant to the provisions hereof, or (B) the
            Exercise Price that would have resulted from any issuance of
            Additional Shares of Common Stock between the original adjustment
            date and such readjustment date;

                  (iv) Upon the expiration or termination of any unexercised
            Option, the Exercise Price shall be readjusted to the Exercise Price
            which would have been in effect at the time of such expiration or
            termination had such Option never been issued (but including the
            recalculation of any intervening adjustments), and the Additional
            Shares of Common Stock deemed issued as the result of the original
            issue of such Option shall not be deemed issued for the purposes of
            any subsequent adjustment of the Exercise Price; and

                  (v) In the event of any change in the number of shares of
            Common Stock issuable upon the exercise, conversion or exchange of
            any Option or Convertible Security, including, but not limited to, a
            change resulting from the antidilution provisions thereof, the
            Exercise Price then in effect shall forthwith be readjusted to such
            Exercise Price as would have obtained had the adjustment which was
            made upon the issuance of such Option or Convertible Security (prior
            to such change) been made upon the basis of such change, but no
            further adjustment shall be made for the actual issuance of Common
            Stock upon the exercise or conversion of any such Option or
            Convertible Security.

            (d) Adjustment of Exercise Price Upon Issuance of Additional Shares
      of Common Stock. In the event the Company shall at any time after the
      Original Issue Date issue Additional Shares of Common Stock (including
      Additional Shares of Common Stock deemed to be issued pursuant to
      paragraph (c) above), without consideration or for a consideration per
      share less than the Exercise Price in effect on the date of and
      immediately prior to such issue, then and in such event, such Exercise
      Price shall be reduced, concurrently with such issue, to a price
      (calculated to the nearest cent) calculated as follows:

                  (i) The adjusted Exercise Price shall be equal to a fraction:
            (A) the numerator of which shall be the number of shares of Common
            Stock outstanding immediately prior to such issue (including shares
            described in clause (ii) below), plus the number of shares of Common
            Stock which the aggregate consideration received by the Company for
            the total number of Additional Shares of Common Stock so issued
            would purchase at such Exercise Price; and (B) the denominator of
            which shall be the number of shares of Common Stock outstanding
            immediately prior to such issue (including


                                       5
<PAGE>
            shares described in clause (ii) below) plus the number of such
            Additional Shares of Common Stock so issued.

                  (ii) For the purposes of clause (i), the number of shares of
            Common Stock outstanding immediately prior to such issue shall be
            calculated on a fully diluted basis, as if all Convertible
            Securities had been fully converted into shares of Common Stock
            immediately prior to such issuance and the Warrant and any other
            outstanding Options had been fully exercised immediately prior to
            such issuance (and any resulting Convertible Securities fully
            converted into Common Stock) as of such date.

                  (iii) The applicable Exercise Price shall not be reduced at
            the time of any issuance of Additional Shares of Common Stock if the
            amount of such reduction would be an amount less than $0.01, but any
            such amount shall be carried forward and reduction with respect
            thereto shall be made at the time and together with any subsequent
            reduction which, together with such amount and any other amounts so
            carried forward, shall aggregate $0.01 or more.

            (e) Determination of Consideration. For purposes of paragraph (d),
      the consideration received by the Company for the issue of any Additional
      Shares of Common Stock shall be computed as follows:

                  (i) Cash and Property: Such consideration shall:

                        (A) insofar as it consists of cash, be computed at the
                  aggregate of cash received by the Company;

                        (B) insofar as it consists of property other than cash,
                  be computed at the fair market value thereof at the time of
                  such issue, as determined in good faith by the Board of
                  Directors; and

                        (C) in the event Additional Shares of Common Stock are
                  issued together with other shares or securities or other
                  assets of the Company for consideration which covers both, be
                  the proportion of such consideration so received, computed as
                  provided in clauses (A) and (B) above, as determined in good
                  faith by the Board of Directors.

                  (ii) Options and Convertible Securities. The consideration per
            share received by the Company for Additional Shares of Common Stock
            deemed to have been issued pursuant to paragraph (c), relating to
            Options and Convertible Securities, shall be determined by dividing:

                        (A) the total amount, if any, received or receivable by
                  the Company as consideration for the issue of such Options or
                  Convertible Securities, plus the minimum aggregate amount of
                  additional consideration (as set forth in the instruments
                  relating thereto, without regard to any provision contained
                  therein for a subsequent adjustment of such consideration)
                  payable to the Company upon the exercise of such Options or
                  the conversion or exchange of such Convertible Securities, or
                  in the case of Options for Convertible Securities, the
                  exercise of such Options for Convertible Securities and the
                  conversion or exchange of such Convertible Securities; by

                        (B) the maximum number of shares of Common Stock (as set
                  forth in the instrument relating thereto, without regard to
                  any provision contained therein for a subsequent adjustment of
                  such number) issuable upon the exercise of such Options or the
                  conversion or exchange of such Convertible Securities.


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<PAGE>
            (f) Certificate as to Adjustments. Upon the occurrence of each
      adjustment or readjustment of the Exercise Price pursuant to this Section
      7, the Company at its expense shall promptly compute such adjustment or
      readjustment in accordance with the terms hereof and furnish to the Holder
      a certificate setting forth such adjustment or readjustment and showing in
      detail the facts upon which such adjustment or readjustment is based. The
      Company shall, upon the written request at any time of the Holder, furnish
      or cause to be furnished to such holder a like certificate setting forth
      (i) such adjustments and readjustments, (ii) the Exercise Price at the
      time in effect, and (iii) the number of shares of Common Stock and the
      amount, if any, of other property which at the time would be received upon
      the exercise of the Warrant.

      8. No Rights as a Shareholder. This Warrant does not entitle the Holder to
any voting rights or other rights as a shareholder of the Company prior to
exercise of this Warrant and the payment for the Shares so purchased.
Notwithstanding the foregoing, the Company agrees to transmit to the Holder such
information, documents and reports as are generally distributed to holders of
the capital stock of the Company concurrently with the distribution thereof to
the shareholders. Upon valid exercise of this Warrant and payment for the Shares
so purchased in accordance with the terms of the Warrant, the Holder shall be
deemed a shareholder of the Company.

      9. Sale or Transfer of the Warrant; Legend. The Warrant and the Shares
shall not be sold or transferred unless either (i) they first shall have been
registered under the Act, or (ii) the Company first shall have been furnished
with an opinion of legal counsel reasonably satisfactory to the Company to the
effect that such sale or transfer is exempt from the registration requirements
of the Act. Each certificate representing any Warrant shall bear the legend set
out on page 1 hereof. Each certificate representing any Shares shall bear a
legend substantially in the following form, as appropriate:

            THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR
            INVESTMENT AND NOT WITH A VIEW TO, OR IN CONNECTION WITH, THE SALE
            OR DISTRIBUTION THEREOF. NO SUCH SALE OR DISPOSITION MAY BE EFFECTED
            WITHOUT AN EFFECTIVE REGISTRATION STATEMENT RELATED THERETO OR AN
            OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE COMPANY THAT SUCH
            REGISTRATION IS NOT REQUIRED UNDER THE SECURITIES ACT OF 1933, AS
            AMENDED.

Such Warrant and Shares may be subject to additional restrictions on transfer
imposed under applicable state and federal securities law.

      10. Put Right. Commencing on December 31, 2004, and prior to the
Expiration Date, the Holder shall have the right, exercised by the delivery of
written notice to the Company (a "Put Notice"), to require the Company to cancel
the unexercised portion of this Warrant, and all related rights in exchange for
a cash payment (the "Put Payment") equal to $0.3525 per share payable to the
Holder within ten (10) days of receipt by the Company of the Put Notice and the
original Warrant for cancellation.

      11. Call Option. At any time during the one year period following the
indefeasible payment in full in cash or cash equivalents of the Credit
Obligations, and prior to June 30, 2004, the Company shall have the right
exercised by the delivery of written notice to the Holder (a "Call Notice") to
cancel this Warrant and the purchase rights hereunder in exchange for a cash
payment (the "Call Payment") equal to $0.5288 per share, payable to the Holder
within five (5) days after delivery by the Company of the Call Notice, provided
however, that any payment made pursuant to this Section 11 may only be made out
of a New Financing Source. Notwithstanding anything to the contrary contained
herein, the Holder shall be entitled to exercise this Warrant in whole or in
part at any time after the receipt of the Call Notice until the receipt by the
Holder of the Call Payment. In the event that the Holder chooses to exercise all
or a portion of the Warrant after receipt of the Call Notice, the Company shall
have the option to rescind such Call Notice or to exercise its call option with
respect to that portion of the Warrant


                                       7
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which remains unexercised through the delivery of a pro rata portion of the Call
Payment. The Company shall have the right to exercise the call option set forth
herein one time only.

      12. Modifications and Waivers. This Warrant may not be changed, waived,
discharged or terminated except by an instrument in writing signed by the party
against which enforcement of the same is sought.

      13. Notices. Any notice, request or other document required or permitted
to be given or delivered to the Holder or the Company shall be sufficiently
given or made if sent by registered or certified mail, postage prepaid,
addressed to the parties as provided below:

          If to Holder:     Fleet National Bank
                            100 Federal Street, 6th Floor
                            MA DE 10006A
                            Boston, MA  02110
                            Attn:   Michael F. O'Neill
                            Senior Vice President

          with a copy to:

                            Brown, Rudnick, Freed & Gesmer
                            One Financial Center
                            Boston, MA  02111
                            Attn:  William R. Baldiga, Esquire
                                   Mary D. Bucci, Esquire

          If to Company:    Nextera Enterprises, Inc.
                            4 Cambridge Center
                            Cambridge, MA 02142
                            Attn:  Michael P. Muldowney,
                                   Chief Financial Officer

          with a copy to:   Maron & Sandler
                            844 Moraga Drive
                            Los Angeles, CA  90049
                            Attn:   Stanley E. Maron, Esquire

      14. Loss, Theft, Destruction or Mutilation of Warrant. The Company
covenants with the Holder that upon its receipt of evidence reasonably
satisfactory to the Company of the loss, theft, destruction or mutilation of
this Warrant or any stock certificate and, in the case of any such loss, theft
or destruction, of an indemnity or security reasonably satisfactory to it, and
upon reimbursement to the Company of all reasonable expenses incidental thereto,
and upon surrender and cancellation of this Warrant or stock certificate, if
mutilated, the Company will make and deliver a new Warrant or stock certificate,
of like tenor, in lieu of the lost, stolen, destroyed or mutilated Warrant or
stock certificate.

      15. Representations and Warranties of Holder. By accepting this Warrant,
the Holder represents and warrants that it is acquiring this Warrant and the
Shares for its own account, for investment and not with a view to, or for sale
in connection with, any distribution thereof or any part thereof. Holder
represents and warrants that it is (a) experienced in the evaluation of
businesses similar to the Company, (b) is able to fend for itself in the
transactions contemplated by this Warrant, (c) has such knowledge and experience
in financial and business matters as to be capable of evaluating the merits and
risks of an investment in the Company, (d) has the ability to bear the economic
risks of an investment in the Company, (e) has been furnished with or has had
access to such information as is specified in subparagraph (b)(2) of Rule 502
promulgated under the Act and (f) has been afforded the


                                       8
<PAGE>
opportunity to ask questions of and to receive answers from the Company and to
obtain any additional information necessary to make an informed investment
decision with respect to an investment in the Company. The Holder further
represents that it is an "accredited investor" as defined in Rule 501(a) of
Regulation D under the Act.

      16. Representations and Warranties of Company. The Company represents
that:

                  (a) The execution and delivery of this Warrant has been duly
            authorized by the Company's Board of Directors and constitutes the
            legal, valid and binding obligation of the Company enforceable
            against the Company in accordance with its terms, except as
            enforcement thereof may be limited by bankruptcy, insolvency, or
            other laws affecting the enforcement of creditors' rights in general
            and except that the enforceability of the obligations hereunder is
            subject to general principals of equity (regardless of whether such
            enforceability is considered in a proceeding at equity or at law).
            Neither the execution nor the delivery of this Warrant, nor
            fulfillment of nor compliance with the terms and provisions of this
            Warrant, nor the issuance of Shares upon exercise of the Warrant,
            will violate the terms of the certificate of incorporation or
            by-laws of the Company or, to the best of the Company's knowledge,
            any agreement (including any agreement with stockholders),
            instrument, judgment, decree or statute to which the Company is
            subject.

                  (b) As of December 31, 2002, the authorized capital stock of
            the Company consisted of (i) 99,300,000 shares of Common Stock,
            $0.001 par value per share, 95,000,000 shares of which are
            designated as Class A Common Stock, of which 31,885,896 shares are
            issued and outstanding, and 4,300,000 shares of which are designated
            as Class B Common Stock, of which 3,869,570 shares are issued and
            outstanding, and (ii) 10,000,000 shares of Preferred Stock, $0.001
            par value per share 600,000 shares of which are designated as Series
            A Cumulative Convertible Preferred Stock, of which 39,544 shares are
            issued and outstanding.

                  (c) Except as set forth in subparagraph (b) above, and in
            registration statements filed by the Company under the Act or in any
            report filed by the Company under the Securities Exchange Act of
            1934, as amended, the Company has not authorized any rights (either
            preemptive or other) or options to subscribe for or purchase from
            the Company, or any warrants or other agreements providing for or
            requiring the issuance by the Company of, any capital stock or any
            securities convertible into or exchangeable for its capital stock.

                  (d) Sufficient shares of authorized but unissued shares of
            Common Stock of the Company have been reserved by appropriate
            corporate action with the prospective exercise of the Warrant, and,
            the issuance of either the Warrant or the shares of Common Stock
            upon exercise of the Warrant will not require any further corporate
            action by the stockholders or directors of the Company, will not be
            subject to preemptive rights (unless the exercise of the same has
            been irrevocably waived) in any present stockholders of the Company
            and will not conflict with any provision of any agreement to which
            the Company is a party or by which it is bound, and such Common
            Stock, when issued upon exercise of the Warrant in accordance with
            its terms, will be duly authorized, fully paid and non-assessable.

      17. Registration Rights.

                  (a) Piggy Back Registration Rights. If (but without any
            obligation to do so) the Company shall determine to register (a
            "Company Registration") any of its securities for its own account or
            for any other person (other than a registration under the Act of
            shares issued in connection with any acquisition of any entity or
            business, shares issuable solely upon the exercise of stock options,
            or shares issuable solely pursuant to


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<PAGE>
            employee benefit plans or arrangements, including registration
            statements on Form S-4, S-8 or any successor form), the Company
            shall do the following:

                        (i) promptly give the Holder written notice thereof
                  (which shall include a list of the jurisdictions in which the
                  Company intends to attempt to register or qualify such
                  securities under the applicable blue sky or other state
                  securities laws); and

                        (ii) include among the securities which it then
                  registers or qualifies all Registrable Securities (as defined
                  below) specified in a written request or requests, made within
                  fifteen (15) days after receipt of the written notice from the
                  Company, by the Holder. The Holder shall have the right to
                  withdraw its request for inclusion of its Registrable
                  Securities in any registration statement by giving written
                  notice to the Company of its request to withdraw. The Company
                  may withdraw a Company Registration at any time prior to the
                  time it becomes effective whether or not the Holder has
                  elected to include Registrable Securities (as defined below)
                  in such registration. For purposes of this Warrant, the term
                  "Registrable Securities" shall mean all shares of Common Stock
                  issued and issuable upon exercise of the Warrant; provided
                  however, that shares of Common Stock which are "Registrable
                  Securities" shall cease to be Registrable Securities (a) upon
                  any sale pursuant to a registration statement under the Act,
                  Section 4(1) of the Act or Rule 144 promulgated under the Act
                  or (b) at such time as such shares of Common Stock are freely
                  saleable under Rule 144(k) promulgated under the Act (or a
                  successor provision).

                  (b) Limitations of Registration. If and to the extent that the
            Holder shall have, at the time of the delivery of the written
            request referred to in subparagraph (a) above, no present intention
            of selling or distribution, the Company shall be obligated to effect
            such registration, qualification or compliance with respect to the
            Holder's Registrable Securities only if and to the extent, in each
            case, that such registration, qualification and compliance are at
            the time permitted by the applicable statutes or rules and
            regulations thereunder or the practices of the governmental
            authority concerned.

                  (c) Registration Procedures. In the case of each registration,
            qualification or compliance pursuant to this Section 17, the Company
            will keep the Holder advised in writing as to the initiation of
            proceedings for such registration, qualification and compliance and
            as to the completion thereof, and will advise the Holder, upon
            written request, of the progress of such proceedings. At the expense
            of the Company, the Company will (i) keep such registration,
            qualification and compliance current and effective for a period of
            the earlier of (A) 120 days, or (B) until the Holder has completed
            the distributions relating thereto, including, without limitation,
            the filing of post-effective amendments and supplements to any
            registration statement or prospectus, as necessary to permit the
            sale or distribution of Registrable Securities not theretofore sold
            or distributed, and (ii) take all necessary action under any
            applicable blue sky or other state securities laws to permit such
            exercise, sale or distribution, all as reasonably requested by such
            Holder; provided, however, that the Company shall not be required in
            connection therewith to qualify as a foreign corporation in any
            jurisdiction in which it is not now so qualified or to take any
            action that would subject it to general consent to service of
            process or taxation. The Company shall not be required to file,
            cause to become effective or maintain the effectiveness of any
            registration statement that contemplates a distribution of
            securities on a delayed or continuous basis pursuant to Rule 415
            under the Act.

                  (d) Registration Rights. Anything to the contrary in Section
            17 notwithstanding, in connection with any Company Registration, the
            Company shall not be


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<PAGE>
            required to include any of the Holder's Registrable Securities in
            such Company Registration unless the Holder accepts the terms of the
            underwriting as agreed upon between the Company and the underwriters
            selected by it (or by other persons entitled to select the
            underwriters), and then only in such quantity as the underwriters
            determine in their sole discretion will not jeopardize the success
            of the offering by the Company or will not adversely affect the
            aggregate proceeds to the Company from the offering. If the total
            amount of securities, including Registrable Securities and all other
            securities requested to be included in such offering by any
            stockholder of the Company, exceeds the amount of securities that
            the underwriters determine in their sole discretion is compatible
            with the success of the offering or the aggregate proceeds to the
            Company from the offering, then the number of Shares to be offered
            for the account of the Holder and all such other persons
            participating in such registration shall be reduced (to zero if
            necessary) or limited pro rata in proportion to the respective
            number of Shares requested to be registered by the Holder and each
            other person to reduce the total number of Shares requested to be
            included in such offering to the number of Shares, if any,
            recommended by such underwriters.

                  (e) Indemnification. The Company will indemnify, defend and
            hold harmless the Holder to the fullest extent that such agreement
            is enforceable under applicable law against all claims, losses,
            damages and liabilities (or actions in respect thereof) arising out
            of or based on any untrue statement (or alleged untrue statement) of
            material fact contained therein (or in any related registration
            statement, notification or the like) or any omission (or alleged
            omission) to state therein a material fact required to be stated
            therein or necessary to make the statements therein not misleading,
            or any violation by the Company of any rule or regulation
            promulgated under the Act applicable to the Company and relating to
            action or inaction required of the Company in connection with any
            such registration, qualification or compliance, and will reimburse
            the Holder for any legal or any other expenses reasonably incurred
            in connection with investigating or defending any such claim, loss,
            damage, liability or action provided, however, that the Company will
            not be liable in any such case to the extent that any such claim,
            loss, damage or liability arises out of or is based on any untrue
            statement or omission based upon written information furnished to
            the Company by an instrument duly executed by the Holder and stated
            to be specifically for use therein.

                  (f) The Holder will indemnify, defend and hold harmless the
            Company to the fullest extent that such agreement is enforceable
            under applicable law against all claims, losses, damages and
            liabilities (or actions in respect thereof) arising out of or based
            on any untrue statement (or alleged untrue statement) of material
            fact contained therein (or in any related registration statement,
            notification or the like) or any omission (or alleged omission) to
            state therein a material fact required to be stated therein or
            necessary to make the statements therein not misleading, or any
            violation by the Holder of any rule or regulation promulgated under
            the Act applicable to the Holder and relating to action or inaction
            required of the Holder in connection with any such registration,
            qualification or compliance, and will reimburse the Company for any
            legal or any other expenses reasonably incurred in connection with
            investigating or defending any such claim, loss, damage, liability
            or action, in each case to the extent (and only to the extent) that
            such claims, losses, damages, liabilities and actions relate to
            reliance on any untrue statement or omission based upon written
            information furnished to the Company by an instrument duly executed
            by the Holder and stated to be specifically for use in the
            registration statement, provided, however, that such Holder's
            obligations hereunder shall be limited to an amount equal to the
            proceeds received by such Holder of the Registrable Securities sold
            in such registration.

                  (g) Notwithstanding the foregoing, to the extent that the
            provisions on indemnification contained in the underwriting
            agreement entered into in connection with a


                                       11
<PAGE>
            Company Registration are in conflict with the provisions of this
            Section 17, the provisions in the underwriting agreement shall
            control.

      18. Binding Effect on Successors. This Warrant shall be binding upon any
corporation succeeding the Company by merger, consolidation or acquisition of
all or substantially all of the Company's assets, and all of the obligations of
the Company relating to the Shares issuable upon exercise of this Warrant shall
survive the exercise and termination of this Warrant and all of the covenants
and agreements of the Company shall inure to the benefit of the successors and
assigns of the Holder.

      19. Amendments. No approval, consent, amendment or waiver of this
Agreement shall be effective unless in writing and signed by the Company and
Holder.

      20. Counterparts. This Agreement may be executed in any number of
counterparts and each such counterpart shall for all purposes be deemed to be an
original, and all such counterparts shall together constitute but one and the
same instrument.

      21. Governing Law. This Warrant shall be construed and enforced in
accordance with, and the rights of the parties shall be governed by, the laws of
the Commonwealth of Massachusetts.

      22. Entire Agreement. This Warrant constitutes the entire agreement among
the parties hereto pertaining to the subject matter hereof, and any and all
other written or oral agreements relating to the subject matter hereof existing
among any of the parties hereto are expressly cancelled, including, but not
limited to, the Prior Warrant.


                                       12
<PAGE>
      IN WITNESS WHEREOF, the parties have caused this Warrant to be executed by
their duly authorized representatives as of the date first above written.

                                            NEXTERA ENTERPRISES, INC.,
                                            as Company

                                            By: /s/ Michael P. Muldowney
                                               ---------------------------------
                                                Michael P. Muldowney
                                                Chief Financial Officer

                                            FLEET NATIONAL BANK,
                                            as Agent, Lender and Holder

                                            By: /s/ Michael F. O'Neill
                                               ---------------------------------
                                                Michael F. O'Neill
                                                Senior Workout Officer


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