Add a user to the “Team Foundation Service Accounts” group in TFS

Here is what you do:

1. Open the TFS Admin Console
2. Click on the Applciation Tier in the left tree
3. In the "Administration Console Users" find your user (assuming it is there)
4. Select your user, and then select "Reapply" to the right of the box
5. Click on Advanced Features in the dialog box that appears.
6. Make sure "Add required permissions to change service accounts" is selected.
7. Select OK