This indicates a possible attack against a cross-site-scripting vulnerability in Microsoft Unified Access Gateway.
This vulnerability is due to an error when the vulnerable software handles a crafted HTTP request. An attacker can exploit this by enticing a user to follow a malicious web link to send a crafted HTTP request to UAG server.
Forefront Unified Access Gateway 2010
Forefront Unified Access Gateway 2010 Update 1
Forefront Unified Access Gateway 2010 Update 2
Cross Site Scripting
Apply the patch supplied by the vendor: