You configure Microsoft Forefront Unified Access Gateway 2010 to use a custom URL logoff page. When a user logs off, the custom URL logoff page is not displayed, and the user receives an internal 500 error.
This problem occurs because of an issue in the CustomUpdate customization framework.
To resolve this problem, install Service Pack 4 for Microsoft Forefront Unified Access Gateway 2010.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
See the terminology Microsoft uses to describe software updates.