ISA Server 2004 may randomly stop responding to new TCP traffic

Microsoft Internet Security and Acceleration (ISA) Server 2004 randomly stops responding to new TCP traffic. This problem occurs if the following conditions are true:

• You have a downstream server that is running ISA Server 2004.
• The downstream server is chained to an upstream server.
• The downstream server has a Web filter that uses the WriteClient function.
• Some clients send Secure Sockets Layer (SSL) requests through the downstream server.

Internet Control Message Protocol (ICMP) packets can still pass through the downstream server. The TCP connections that are already established continue to work.

To resolve this problem, apply the ISA Server 2004 hotfix package that is dated March 8, 2007. For more information about this hotfix package, click the following article number to view the article in the Microsoft Knowledge Base:

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

To work around this problem, increase the default number of worker threads. To do this, follow these steps:

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\system\CurrentControlSet\Services\fwsrv\parameters
3. Point to New, and then click DWORD Value.
4. Type MinCtrlThreads as the registry entry name, and then press ENTER.
5. Double-click MinCtrlThreads.
6. Type an appropriate value in the Value data text box, and then click OK.
   
   Note This value represents the number of worker threads that are created when the ISA Server process starts. The default value is set to 5. To resolve the problem, increase this value. For example, set this value to 256.

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