Problem with CleanBuildPolicy in the December CTP
When you try to configure a new checkin policy, you will get an error regarding the CleanBuildPolicy. That policy has a problem due to it or one of its dependencies not being properly signed. You can work around the problem by removing it from the registry by deleting the following key. HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Hatteras\Checkin Policies\CleanBuildPolicy
How to write a checkin policy
If you would like to write your own checkin policy, you'll want to read Jim Presto's blog. He has posted information on how to do it along with the code.
What is the Team Build error dialog about?
If you get a message dialog about a problem with Team Build, you can safely ignore it. It's not fully functional in the December CTP.