<PAGE>
                                                                    Exhibit 10.1
                                                                    ------------

                         400 RIVER LIMITED PARTNERSHIP
                             2101 ROSECRANS AVENUE
                                   SUITE 5252
                          EL SEGUNDO, CALIFORNIA 90402
                 Telephone (310) 607-0003   Fax (978) 607-3005

November 12, 2002

Via Telecopy and Federal Express
--------------------------------
Mr. Arthur Becker
ClearBlue Technologies, Inc.
20 East 66th Street
2nd Floor
New York, NY 10021

Re:   400 Minuteman Road, Andover, Massachusetts (the "Property")

      Escrow # 2251-25171 with Chicago Title Insurance Company (the "Escrow")

      Transactions Involving 400 River Limited Partnership ("River"), Farm
      Associates Limited Partnership ("Farm"), NaviSite, Inc. ("NaviSite"),
      and ClearBlue Technologies, Inc. ("ClearBlue") (collectively, the
      "Transactions")

Dear Arthur:

As you know, we closed the first leg of the Transactions on 9/11/2002. Pursuant
to the Undertakings Agreement dated 9/11/2002 among River, Farm and ClearBlue
(the "Undertakings Agreement"), the Escrow Agreement dated 9/11/2002 among
River, Farm, ClearBlue and Chicago Title Insurance Company (the "Escrow
Agreement"), and the Cash Escrow Letter Agreement dated 9/11/2002 among River,
ClearBlue and Chicago Title Insurance Company, we deposited certain documents
(most of which were not executed) into the Escrow, ClearBlue deposited
$999,973.20 into the Cash Escrow with Chicago Title Insurance Company, and
ClearBlue delivered a $1,000,000 Promissory Note dated 9/11/2002 to River (the
"Note").

We hereby amend the Transactions, and certain of the documents evidencing the
Transactions, as follows:

1.  The Note is amended to delete the provisions regarding accrual of interest
and to increase the face amount of the Note to Two Million Dollars ($2,000,000).
River will instruct Chicago Title to return to ClearBlue the $999,973.20
deposited into the Cash Escrow by ClearBlue (together with any accrued and
unpaid interest thereon) when and if Clear Blue delivers to River a new Note for
Two Million Dollars ($2,000,000) and otherwise on the same terms as the existing
Note, duly executed and authorized by ClearBlue (at which time River also will
deliver back to ClearBlue, or destroy, the existing Note).

2.  All parties have agreed that the initial 6-day closing period described in
the Undertakings Agreement and the Escrow Agreement is extended from 11/12/2002
until 1/31/2003, and that no party is prejudiced by agreeing to such extension
(i.e., the documents evidencing the Transactions, as modified hereby, are still
in full force and effect, subject to the satisfaction of the conditions to
closing as set forth therein).

3.  If we close under the Undertakings Agreement after 11/12/2002 and on or
before 1/31/2003, 400 River will reimburse to NaviSite one-half of the base
rent, Taxes and insurance costs paid by NaviSite to River under the existing
Lease of the Property between NaviSite and River for the period 11/13/2002 until
the closing occurs.

4.  If NaviSite is not in default under the New Lease beyond applicable notice
and core periods therein, and, on or before August 1, 2003, Farm enters into a
lease of at least 35,000 square feet of the Property with a new tenant other
than NaviSite or its affiliates and such lease has become enforceable in
accordance with its terms (and the new tenant either has occupied its new space
to conduct business or has paid its first month's rent under its new lease),
Farm will pay to NaviSite an additional Four Hundred Thousand Dollars
($400,000).


<PAGE>

5.  ClearBlue and NaviSite have requested and Farm has agreed that NaviSite will
have the right, but not the obligation, to lease additional space on the 2nd
floor of the Building at 400 Minuteman Road as follows. NaviSite may exercise
this right only by delivering unconditional written notice of exercise to Farm
on or before 5:00 PM Eastern Time on December 1, 2002. Time is of the essence,
and if for any reason this unconditioned exercise notice is not delivered as and
when required, NaviSite will have no right to lease additional space in the
Building. If this unconditional exercise notice is delivered as and when
required, the new Lease between Farm, as landlord and NaviSite, as tenant, which
is one of the unexecuted documents deposited into the Escrow pursuant to the
Undertakings Agreement (the "New Lease"), will be deemed to have been modified
to add to NaviSite's initial leased premises on the 1st floor of the Building
11,500 r.s.f. of additional office space on the 2nd floor of the Building, being
the area in the Southeast corner of the 2nd floor that formerly housed the
cafeteria (the "New Space) on the same terms (e.g., the same rental rate per
square foot of rentable area) as the rest of the leased premises, for a total
of 88,000 r.s.f. under the New Lease, and NaviSite's Tenant's Percentage will be
increased to 57.52%. Regardless of whether NaviSite exercises its right to lease
the New Space, the New Lease is hereby modified by deleting Rider #2 thereto and
attaching Rider #2 attached hereto.

6.  The Temporary License Agreement between Farm, as licensor, and NaviSite, as
licensee, which is one of the unexecuted documents deposited into the Escrow
pursuant to the Undertakings Agreement (the "Temporary License"), is modified by
replacing the phrase "six (6) months from the date hereof" in Section 2(b) of
the Temporary License with the phrase "February 1, 2003", with the intent that
NaviSite will vacate the 2nd floor of the Building and the license granted
thereunder will terminate no later than that date.

Please have ClearBlue sign below to show its agreement to these changes and its
agreement to promptly execute and deliver conforming amendments to (or
replacements of) the following documents: the Undertakings Agreement; the Escrow
Agreement; the Cash Escrow Agreement; the Note; the Purchase and Sale Agreement;
the Temporary License; and the New Lease. Please deliver back to me at least one
fully-executed counterpart original of this Letter Agreement. When fully
executed, this Letter Agreement will be deemed to amend the Transactions and the
documents described above, and will also serve as a modification of the escrow
instructions to Chicago Title. Please call if you have any questions.

Regards,

400 RIVER LIMITED PARTNERSHIP             FARM ASSOCIATES LIMITED PARTNERSHIP
By: Niuna-400 River, Inc.,                By: Finca-Farm, Inc., general partner
    general partner

    By: /s/ John Kusmiersky                   By: /s/ John Kusmiersky
        -----------------------                   -----------------------
        Name:  John Kusmiersky                    Name:  John Kusmiersky
        Title: President                          Title: President

Agreed:                                   Agreed:

CLEARBLUE TECHNOLOGIES, INC.              NAVISITE, INC.

By: /s/ Arthur Becker                     By: /s/ Kevin H. Lo
    -----------------------                   -----------------------
    Name:  Arthur Becker                      Name:  Kevin H. Lo
    Title: Director                           Title: CFO
    Authorized Officer                        Authorized Officer

<PAGE>

Mr. Arthur Becker
November 10, 2002
Page 2
NAVISITE LETTER MODIFICATION OF DOCS #9 - 1112021.doc

                                    RIDER #2

Miscellaneous Changes
---------------------

This Rider #2 changes, supplements and modifies certain provisions of this
Lease, and if there is any conflict between this Rider #2 and the rest of this
Lease, this Rider will control.

A.   Section 1.1(c) is deleted and is replaced by the following:

     "Premises: The Ground Floor of the Building (excluding the Lobby Area but
     including the MDF Rooms as described in Section 24.2(b)), and the Penthouse
     area of the Building, all as shown in Exhibit "A-1" agreed to contain
     76,500 square feet of rentable area."

B.   In Section 1.3, the words "Landlord's Work and/or" are deleted from the
first line.

C.   In Section 3, Tenant's Moveable Property will include, and Non-Removed
Property will not include, Tenant's network switchgear and associated cabling.

D.   In Section 5(b), the words "Bank of Boston" are replaced by the words
"Fleet Bank".

E.   In Section 8.1(a), the figure "7,000,000.00" is replaced by the figure
"5,000,000.00".

F.   In Section 10, the first two sentences are deleted and are replaced by the
following:

     "Tenant will pay when due to the furnishing parties all fees and costs for
     utility services, and meters and equipment, furnished to the Premises,
     including, without limitation, telephone, electricity, HVAC, sewer, water
     and gas (if furnished). However, when and if Landlord leases to other
     tenants who then occupy the Building, Landlord will install, at its
     expense, meters, submeters, or Intellimeters or their equivalent to measure
     the electricity actually used within the Premises and charge Tenant
     according to that actual use."

G.   In Section 12.1, the following are added as part of Landlord's obligations
to repair and maintain: the Lobby Area, the Atrium, the base building Systems
and Equipment that serve the common areas (but not the Premises), the roof, and
the exterior window systems.

H.   Section 12.2 is deleted and is replaced by the following:

     "12.2 Tenant's Obligations. Except for Landlord's obligations in Section
     12.1 and as set forth immediately below, Tenant will maintain and repair
     the Premises and all Systems and Equipment serving the Premises, including
     the following, regardless of whether they are within or outside the
     Premises: the existing backup generators, existing telephone switches,
     switch gear, holding tanks, paralleling gear, switch gear, UPS equipment,
     batteries or any power distribution equipment, and associated Systems and
     Equipment, and the life safety Systems and Equipment (but Landlord will
     reimburse to Tenant the reasonable cost of repairing, maintaining or
     replacing minor items of the life safety Systems and Equipment in other
     tenant spaces or in the common areas, such as fire extinguishers, exit
     lighting, or fire alarms), in a first-class manner (including replacement
     thereof if and when necessary), and keep the Premises in good order and
     condition, including, without limitation, Tenant's Movable Property, all
     doors, windows, window treatments, wall coverings, floor coverings,
     non-structural portions of the ceiling, floor and walls, and Tenant's
     Alterations (unless otherwise requested by Landlord). Tenant will not be
     required to repair or maintain the elevators. Subject to Landlord's prior
     consent, which will not be unreasonably withheld, Tenant may select a
     cleaning company of its choice to clean the Premises at Tenant's sole cost.
     In furtherance of Tenant's maintenance and repair obligations, Landlord
     will assign to Tenant, or cooperate in a commercially reasonable manner
     with Tenant in enforcing, any guarantees or warranties applicable to the
     Building and the Systems and Equipment. If Tenant does not repair and
     maintain as required above or in

<PAGE>

MR. ARTHUR BECKER
November 10, 2002
Page 2
NAVISITE LETTER MODIFICATION OF DOCS #9 - 1112021.doc

     accordance with applicable Laws, in addition to any other rights of
     Landlord hereunder, Landlord may contract with outside contractors to
     repair and maintain all or parts of the Systems and Equipment that Tenant
     is otherwise required to repair and maintain, and if so, Tenants will pay
     to Landlord the reasonable costs thereof."

H.   In Section 13.2, the words "or approvals" is added in the second line.

I.   Section 13.6 is deleted and is replaced by the following:

     "13.6 Conversion to Office Space. Subject to the following and the rest of
     this Article and this Lease (but not Section 13.1(e), which will not
     apply), Tenant will have the right to convert portions of the interior of
     the Premises from their current use as a data center to office use (the
     space so converted is called the "Office Space"). The Office Space will not
     include the MDF Rooms or the Penthouse, as defined in Section 24.2(b).
     Tenant will employ licensed mechanical engineers, architects and
     contractors it selects subject to the reasonable approval of Landlord, such
     approval not to be unreasonably withheld or delayed, for the design and
     construction of the Office Space, and will construct the Office Space in
     accordance with the terms of this Lease, and the plans, specifications and
     recommendations approved by Landlord subject to this Lease, subject to
     compliance with applicable Laws. Tenant will be solely responsible for the
     timely payment of all fees and costs for said engineers, architects and
     contractors, and for the reasonable costs of any engineers or architects
     hired by Landlord to review Tenant's plans and specifications and supervise
     such work, and all other costs and other Liabilities in connection with the
     design and construction of the Office Space and will indemnify Landlord and
     its Affiliates therefor and defend and hold them harmless therefrom."

J.   In Section 13.5, Tenant and its Affiliates will be granted both internal
and external access to the rooftop for the purposes described in Section 13.5
subject to Landlord's reasonable rules and regulations as to access and the
other terms of that Section and the rest of this Lease, and provided further
that Tenant will indemnify Landlord and its Affiliates for all damage and other
Liabilities resulting therefrom.

K.   In Section 15.2, the reference to Section 13.8 is changed to Section 13.6.

L.   Section 18.5(a)(i) is deleted and is replaced by the following:

     "(i) A "Tenant Affiliated Entity" means and refers to a person,
     corporation, limited liability company, partnership or other business
     entity or organization which is a parent corporation of Tenant, or a
     subsidiary corporation of Tenant or its parent corporation, or is under
     common control of Tenant or its parent corporation."

M.   The last sentence of Section 19.1 is deleted.

N.   Section 24.2(b) is deleted and is replaced by the following:

     "(b) Notwithstanding Subsection (a) above or anything else to the contrary,
     although the MDF rooms and the Penthouse area of the Premises, all as shown
     in Exhibit "A-1" (the "MDF Rooms," and the "Penthouse," respectively) will
     remain part of the Premises, Tenant understands and agrees that: Tenant's
     use of the MDF Rooms and the Penthouse are non-exclusive, and Landlord may
     allow others to use those areas; Tenant may not alter or reconfigure the
     MDF Rooms and the Penthouse without Landlord's prior written consent nor
     may Tenant close any of them at any time, whether before, during or after
     business hours, or deny access to others permitted by Landlord to use them.
     except to the extent previously approved by Landlord in writing and subject
     to the terms below; and Landlord and its designees will have the right to
     freely access and use the MDF Rooms and the Penthouse and install Systems
     and Equipment therein, subject to the terms below. Access to the MDF Rooms
     and the Penthouse will be subject to the terms of Section 24.2(a) above. In
     no event shall Tenant be subject to or responsible for any Liabilities
     which result from the entry by Landlord, its Affiliates, its guests,
     employees, invitees or contractors or the other tenants of the Building
     into the Premises, including the MDF Rooms or the Penthouse, except to the
     extent that such Liabilities result from the negligence or willful
     misconduct of Tenant."

<PAGE>
MR. ARTHUR BECKER
November 10, 2002
Page 2
NAVISITE LETTER MODIFICATION OF DOCS#9 - 1112021.doc

O.   Section 24.3 is deleted and is replaced by the following:

     "24.3 Brokers. Tenant represents and warrants that it has no written or
     oral agreement with any agent, broker, finder or other person which would
     entitle such a person to a commission or other fee from Landlord in
     connection with this or any related transaction. Landlord represents and
     warrants that it has no written or oral agreement with any agent, broker,
     finder or other person which would entitle such a person to a commission or
     other fee from Tenant in connection with this or any related transaction."

P.   In Paragraph 9 of the Rules and Regulations attached as Exhibit "E" to this
Lease, the following will be added at the end of the first sentence: "(except
for chemicals or vapors used for the existing dry-suppression life safety system
in the Building, which will be permitted provided that Tenant uses them in a
commercially reasonable and customary manner and complies with all applicable
Laws in connection therewith)."

<PAGE>
MR. ARTHUR BECKER
November 2, 2002
Page 2
NAVISITE LETTER SHARE DISTRIBS #2 - 111202.doc

Agreed:                                      Agreed:

CLEARBLUE TECHNOLOGIES, INC.                 NAVISITE, INC.

By: /s/ Arthur Becker                        By: /s/ Kevin H. Lo
    -----------------------                      ----------------------------
    Name:  Arthur Becker                         Name: Kevin H. Lo
    Title: Director                              Title: CFO
    Authorized Officer                           Authorized Officer

Agreed:

By: /s/ Arthur Becker
    -----------------------
    Arthur Becker