[Update 11/26/12] You can get the fix by installing Update 1 (or newer) for Visual Studio 2012: http://www.microsoft.com/visualstudio/eng/downloads.
Some customers, after starting to use Visual Studio 2012 with their existing TFS deployment, have been receiving check-in policy errors having to do with the Changeset Comments policy. The errors look like:
Internal error in Changeset Comments Policy. Error loading the Changeset Comments Policy policy (The policy assembly 'Microsoft.TeamFoundation.PowerTools.CheckinPolicies.ChangesetComments, Version=22.214.171.124, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' is not registered.). Installation instructions: To install this policy, follow the instructions in CheckForComments.cs.
The version number may vary slightly, but for this particular problem, it's always going to start with an 8 or a 9.
With VS 2005 through 2010, to get the Changeset Comments policy, you had to download and install the Team Foundation Power Tools. With VS 2012, the policy is included in the box and requires no additional download. This problem is a bug that was introduced as a part of moving that check-in policy into the product.
For this particular bug, only users using Visual Studio 2012 will be affected. If you have other users in your organization connecting to the same TFS server with VS 2005, 2008, or 2010, then the Changeset Comments policy should be working fine for them.
There is also a simple workaround that you can put in place immediately, as long as you have administrative permissions on your team project. Using a Visual Studio 2010 or 2012 client, navigate to the Team Project Settings for the Team Project that has the Changeset Comments policy configured. Remove the check-in policy from the Team Project, and then immediately re-add it. The fact that you performed this step from a Visual Studio 2010 or 2012 client will re-register the policy on the server as the "10.0.0.0" version, which fixes the problem. Now any client (VS 2005 through VS 2012) will be able to load the policy successfully.
We are including a fix for this problem in the final version of Visual Studio 2012 Update 1. You can read more about Update 1 in Brian's blog post, but the currently available preview release of that update doesn't include this fix.
We apologize for the inconvenience!
Follow me on Twitter at twitter.com/tfsbuck