The Microsoft Firewall service stops unexpectedly if a Web filter is used on a computer that is running ISA Server 2006

On a computer that is running Microsoft Internet Security and Acceleration (ISA) Server 2006, the Microsoft Firewall service stops unexpectedly. This problem occurs if the following conditions are true:

• The http compression filter is configured to use the following settings:
  • The Return Compressed Data option is set to All Networks.
  • The Content Types list includes the Images content type.
  • The Request Compressed Data option is set to All Networks.
• ISA Server has a Web filter that uses the WriteClient function.
• Some clients make requests to retrieve image-file content through ISA Server.

This problem occurs because of an access violation in the W3filter.dll module.

To work around this problem, do not include Images in the Content Types list for compression.

Note Most of the Images content types already include a compression algorithm. Therefore, this workaround does not affect traffic bandwidth.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section. This problem is scheduled to be fixed in ISA Server 2006 Service Pack 1.