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**UNITED      STATES **

**SECURITIES      AND EXCHANGE COMMISSION **

**Washington,      DC 20549 **

**FORM      10-K/A **

**Amendment      No. 1**

**x**
**ANNUAL      REPORT PURSUANT TO SECTION 13 or 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934      **

**For      the fiscal year ended December 31, 2006 **

**OR      **

** ̈**
**TRANSITION      REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934      **

**For      the transition period from             to            **

**Commission      File Number 000-29085 **

**IMPSAT      Fiber Networks, Inc. **

**(Exact      name of registrant as specified in its charter) **

|                                                                                                      |                                                                            |
|-----------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------|
| **Delaware**                                                                                              | **52-1910372**                                                                  |
| **(state                or other jurisdiction of****incorporation                or organization)**  | **(IRS                employer****identification                number)**  |

**Elvira      Rawson de Dellepiane 150 **

**Piso      8, C1107BCA **

**Buenos      Aires, Argentina **

**(5411)      5170-0000 **

**(Address,      including zip code, and telephone number, including area code, of registrant’s      principal executive offices) **

**Securities      registered pursuant to Section 12(b) of the Act: None**

|  **Title                  of Each Class** | **Name                  of Each Exchange****On                  Which Registered** |
|------------------------------------------------|------------------------------------------------------------------------------------|

**Securities      registered pursuant to Section 12(g) of the Act: common stock, par value      $0.01 per share **

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**Amendment      No. 1 to IMPSAT Fiber Networks, Inc.’s Annual Report on Form      10-K**

**For      the Year Ended December 31, 2006**

**EXPLANATORY      NOTE**

**Item 12.**
**Security      Ownership of Certain Beneficial Owners and Management and Related Stockholder      Matters **

**Security      Ownership of Management and Certain Beneficial Owners **

|                                                           |    | **Shares****Beneficially Owned**             |         |
|---------------------------------------------------------------------|--------------|---------------------------------------------------|--------------|
| **Name                and Address of Beneficial Owner**             |    | **Number                of****Total Shares** |    | **Percent****(1)** |   |
| **Common                Stock**                                     |    |                                              |    |   |   |
|                                                                |         |                                              |
| *Beneficial                Owners of more than 5%*                  |    |                                              |    |   |   |
| Morgan                Stanley & Co. Incorporated(2)        |    | 3,165,645                                         |    | 29.8 | % |
| William                R. Huff(3)                                   |    | 2,915,469                                         |    | 22.3 | % |
| Nortel                Networks Limited(4)                           |    | 2,755,108                                         |    | 21.5 | % |
| UBS                Securities LLC(5)                                |    | 1,918,380                                         |    | 18.9 | % |
| James                G. Dinan(6)                                    |    | 1,522,758                                         |    | 14.6 | % |
| Outrider                Management, LLC(7)                          |         | 844,163                                           |         | 8.3 | % |
| SDS                Capital Group SPC, Ltd.(8)                       |    | 534,659                                           |    | 5.3 | % |
|                                                                |         |                                              |
| *Directors                and Executive Officers*                   |    |                                              |    |   |   |
| Ricardo                A. Verdaguer                                 |    | 786,080                                           |    | 7.3 | % |
| Edward                Dartley(3)                                    |    | 2,000                                             |    | 0.0 | % |
| Bryan                E. Bloom(3)                               |         | —                                 |    | —   |    |
| Thomas                Doster IV(2)                                  |    | —                                 |    | —   |   |
| Ignacio                Troncoso                                     |         | 40,000                                            |         | 0.4 | % |
| Héctor                Alonso                                   |    | 209,497                                           |    | 2.0 | % |
| Marcello                Girotti                                     |    | 195,392                                           |    | 1.9 | % |
| Mariano                Torre Gómez                             |    | 205,352                                           |    | 2.0 | % |
| Matias                Heinrich                                      |    | 202,118                                           |    | 2.0 | % |
| Guillermo                V. Pardo                                   |    | 132,913                                           |    | 1.3 | % |
| José                R. Torres                                  |    | 132,913                                           |    | 1.3 | % |
| *All                Directors and Officers as a Group (11 persons)* |    | 1,906,265                                         |    | 16.1 | % |

| (1)   | For                purposes of this table, “beneficial ownership” is determined in accordance                with Rule 13d-3 under the Securities Exchange Act of 1934, pursuant                to                which a person or group of persons is deemed to have “beneficial                ownership” of any shares of common stock that such person has the right to                acquire within 60 days. The percentage of total outstanding for each                stockholder is calculated by dividing (i) the number of shares of                common stock deemed to be beneficially owned by such stockholder                as of                March 15, 2007 by (ii) the sum of (A) the number of shares                of common stock outstanding as of March 15, 2007 plus (B) the                number of shares of our common stock issuable upon the exercise of                options                or warrants or conversion of convertible securities held by such                stockholder that were exercisable or convertible as of March 15, 2007                or will become exercisable or convertible within 60 days thereafter.                This                calculation is required irrespective of the price at which the shares                of                common stock may be acquired. |
|-----------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (2)   | Represents                2,701,511 shares of our common stock, Series B 6% Senior Guaranteed                Convertible Notes due 2011 (“Series B Notes”) convertible into 424,134                shares of our common stock at a conversion price of $20.78, and stock                options for 40,000 shares of our common stock, 30,000 of which are                exercisable at $6.17 per share and 20,000 of which are exercisable                at                $15.00 per share, and 32,546 of which are exercisable at $7.05 per                share.                Mr. Doster is employed in various capacities by Morgan Stanley. He                disclaims any beneficial interest in these shares owned by Morgan                Stanley.                The address for Morgan Stanley is 1585 Broadway, New York, NY 10036. |
|-----------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (3)   | Represents                Series A Notes convertible into 2,046,448 shares of our common stock                at a                conversion price of $13.56, Series B Notes convertible into 548,700                shares                of our common stock at a conversion price of $20.78, and currently                exercisable Warrants to purchase 320,321 shares of our common stock                which                are exercisable at a price of $15.00 per warrant, all of which are                controlled by Mr. William R. Huff through controlled entities:                WRH Partners Global Securities, L.P., W.R. Huff Asset Management                Co.,                L.L.C. and certain other affiliated limited partnerships for their                clients                and/or on behalf of certain separately managed accounts. As of                March 15, 2007, Messrs. Dartley and Bloom were employees of                W.R. Huff Asset Management Co., L.L.C. Messrs. Dartley and Bloom                disclaim any beneficial interest in these shares. The address for                Mr. William R. Huff is c/o W.R. Huff Asset Management Co.,                L.L.C., 1776 On the Green, 67 Park Place, Morristown, New Jersey                07960. |
|-----------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (4)   | Represents                5,199 shares of our common stock and currently exercisable Warrants                to                purchase 2,769,909 shares of our common stock which are exercisable                at a      price of $15.00 per warrant. The address of Nortel is 8200                Dixie Road,                Suite 100, Brampton, Ontario, L6T 5P6 Canada. |
|-----------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (5)   | UBS                Securities LLC, a Delaware limited liability company, is 100%-owned,                directly or indirectly, by UBS AG, a Switzerland entity. By reason                of its                ownership of UBS Securities LLC, UBS AG shares investment and voting                power                with respect to the shares of our common stock held by UBS Securities                LLC.                UBS AG disclaims beneficial ownership of any of the shares of our                common                stock owned by UBS Securities LLC. UBS Securities LLC’s address is 677                Washington Boulevard, Stamford, Connecticut 06901 and UBS AG’s address is                Bahnhofstrasse 45, PO Box CH-8021, Zurich,                Switzerland. |
|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (6)   | Includes                1,276,100 shares of common stock and Series A Notes convertible into                246,658 shares of our common stock, which are exercisable at a price                of                $15.00 per warrant all held by Mr. James G. Dinan, senior                managing member of Dinan Management, L.L.C., through (i) six                controlled entities: York Investment Limited, York Capital Management,                L.P., York Select, L.P., York Select Unit Trust, York Distressed                Opportunities Fund, L.P., and York Offshore Investors Unit Trust;                and                (ii) certain other funds and accounts (“Managed Accounts”) over which                Mr. Dinan has discretionary investment authority. Mr. Dinan is                the President and sole shareholder of JGD Management Corp., a Delaware                corporation, which manages the Managed Accounts. The address for                Mr. James G. Dinan is 350 Park Avenue, 4th Floor, New York, NY 10022. |
|-----------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (7)   | Outrider                Management, LLC is the general partner and investment advisor of                Outrider                Master Fund, LP, a security holder of the issuer. Outrider Management,                LLC                is also an investment advisor and has sole investment discretion                with                respect to an account of HFR EM Outrider Master Trust, a security                holder                of the issuer. The address of Outrider Management, LLC is 455 Market                Street, Suite 1600, San Francisco, CA                94105-2420. |
|-----------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (8)   | SDS                Management, LLC, a Delaware limited liability company, is the investment                manager of SDS Capital Group SPC, Ltd., a Cayman Islands corporation.                Mr. Steven Derby, a United States citizen, is the sole managing                member of SDS Management, LLC. SDS Management, LLC and Mr. Steven                Derby disclaim beneficial ownership of any of the shares of our common                stock owned by SDS Capital Group SPC, Ltd. The address of SDS Capital                Group SPC, Ltd. is c/o SDS Management, LLC, 53 Forest Avenue, 2nd                Floor,                Old Greenwich, Connecticut 06870. |
|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

**Equity      Compensation Plans **

*2003      Stock Incentive Plan.*

*Equity      Compensation Plan Information*

|                                                                         |   | **(a)**                                                                                                                                                                                        |   | **(b)**                                                                                                      |   | **(c)**                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------|--------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------|--------------------------------------------------------------------------------------------------------------|--------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| **Plan                category**                                             |   | **Number                of****securities                to be****issued                upon****exercise                of****outstanding                options****and                rights** |   | **Weighted-average****exercise                price of****outstanding****options                and rights** |   | **Number                of****securities                remaining****available                for future****issuance                under****equity                compensation****plans                (excluding****securities                reflected****in                column (a))** |
| Equity                compensation plans approved by security holders(1)     |   | 1,834,138                                                                                                                                                                                      |   | $                                                                                                            | 14.28  |                                                                                                                                                                                                                                                                                         | 1,052,906 |
| Equity                compensation plans not approved by security holders(2) |   | 40,000                                                                                                                                                                                         |   | $                                                                                                            | 8.38   |                                                                                                                                                                                                                                                                                         | 0 |
| Total                                                                        |   | 1,874,138                                                                                                                                                                                      |   | $                                                                                                            | 14.16  |                                                                                                                                                                                                                                                                                         | 1,052,906 |

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**SIGNATURES      **

|   | **IMPSAT                        FIBER NETWORKS, INC.**  |
|--------|--------------------------------------------------------------|
|   | By:                                                          |       /s/                        RICARDO A.                        VERDAGUER                |
|   |                                                         | **Ricardo                        A. Verdaguer** |
|   |                                                         | **                         President and Chief Executive Officer**  |
|   |                                                         | Date:                        April 16, 2007 |