If you’re running Lab Management with lab machines with XP SP3, you may run into a problem where the Test Agent is never ready for running tests.
The environment was starting up fine and configuring both network isolation as well as the workflow agent. However, the Test Capability was continually not ready – the event logs had a message like this:
Unable to connect to the controller on 'TFSMachine.Domain:6901'. The agent can connect to the controller but the controller cannot connect to the agent because of following reason: An error occurred while processing the request on the server: System.IO.IOException: The write operation failed, see inner exception. ---> System.ComponentModel.Win32Exception: The message or signature supplied for verification has been altered.
Scratching around led me to this rather helpful blog site: Troubleshooting Guide for Visual Studio Test Controller and Agent. The problem is mentioned there – it’s a problem with a Windows hotfix (KB968389) which you simply need to uninstall from the XP Lab machine. Reboot and you’re good to go.