When a client sends an HTTP POST request to a portal in Microsoft Forefront Unified Access Gateway (UAG) 2010, Forefront UAG 2010 may intermittently return the following error message:
The URL you requested cannot be accessed.
You may experience this problem when a client sends an HTTP POST that has 2,047 bytes or 2,048 bytes of header data. This problem occurs more frequently if you publish an Active Directory Federation Services (AD FS) server, because the Secure Association Markup Language (SAML) request adds significantly to the size of the request header.
To work around this problem, you may be able to change the problematic requests so that they send more bytes or fewer bytes of header data.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.