Users receive the following error message when trying to sign in to Microsoft Office Communicator 2007 R2:

Cannot sign in because the server is temporarily unavailable. If the problem persists, contact your system administrator.

If you restart the Microsoft Office Communications Server 2007 R2 front-end server, users can sign in to Office Communicator 2007 R2. However, users are kicked out moments later. This issue occurs when the front-end server is running on a computer with 4GB memory or a multiple of 4GB memory.


This issue occurs because the front-end server is considered to be overloaded on a computer with 4GB memory or a multiple of 4GB memory. This even occurs when there is little traffic on the server.


To resolve this problem, install the following cumulative update:

2404547 Description of cumulative update for Office Communications Server 2007 R2: November, 2010


Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 How to back up and restore the registry in WindowsTo work around this issue, follow these steps to create two registry keys:

  1. Click Start, type Regedit in the search box, and then press ENTER.

  2. Locate and then click the following registry subkey:

    HKEY_LOCAL_MACHINE\ System\CurrentControlSet\Services\RtcSrv\Parameters

  3. On the Edit menu, point to New, and then click DWORD (32 bit) Value.

  4. Type ProxyConnHighMark, and then press ENTER.

  5. Right-click ProxyConnHighMark, and then click Modify.

  6. Type 25000, and then click OK.

  7. On the Edit menu, point to New, and then click DWORD (32 bit) Value.

  8. Type ProxyConnLowMark, and then press ENTER.

  9. Right-click ProxyConnLowMark, and then click Modify.

  10. Type 10000, and then click OK.

  11. Exit Registry Editor.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

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