ISA Server 2006 incorrectly returns an "HTTP 304 Not Modified" response to a proxy client

Microsoft Internet Security and Acceleration (ISA) Server 2006 may incorrectly return an "HTTP 304 Not Modified" response to a proxy client. For example, ISA Server 2006 may return an "HTTP 304 Not Modified" response to a proxy client when the content is changed or is expired.

This problem can occur if the client browser sends a request that includes the "If-Modified-Since" header field.

To resolve this problem, obtain and install the hotfix that is described in the following article in the Microsoft Knowledge Base:

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