Some Web servers that are published in ISA Server 2006 by using the Web Publishing Load Balancing feature may be incorrectly detected as unavailable at random times

In Microsoft Internet Security and Acceleration (ISA) Server 2006, you publish multiple Web servers in a Web farm by using the Web Publishing Load Balancing feature. In this scenario, some published Web servers may be incorrectly detected as unavailable at random times. Over time, ISA Server may stop processing incoming requests for the publishing rule that uses this Web farm.

When this problem occurs, the following alerts may be logged:

• A Web publishing rule stopped forwarding requests to a Web 
  farm because there are currently no servers in the Web farm 
  that can accept requests.

• ISA Server stopped forwarding Web requests through the Web 
  publishing rule <Rule_Name> to the server farm <Web_Farm_Name> 
  because all farm servers are either being drain-stopped or 
  are out of service.

This problem disappears after you restart all ISA Server services or after you change the ISA configurations. However, this problem may appear again after a while.

This problem occurs because the Web Publishing Load Balancing feature cannot create the required thread that is used to update the connection status from the connectivity verifier.

To resolve this problem, apply the hotfix package that is described in the following Microsoft Knowledge Base article:

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