By default, when you publish Active Directory Federation Services (AD FS) 2.0 servers by using Microsoft Forefront Unified Access Gateway (UAG) 2010, the built-in AD FS template is used. However, in a scenario in which this configuration is loaded with approximately 250 concurrent users, the server that is running Forefront UAG may stop responding or crash with "HTTP 503" errors. The "HTTP 503" errors are returned from Internet Information Services (IIS) because the IIS request queues are full.
To resolve this issue, install the rollup package that is described in the following Microsoft Knowledge Base article:
2647899 Rollup 1 for Forefront Unified Access Gateway (UAG) 2010 Service Pack 1 Update 1
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates