I saw this recently using VS2012 & TFS2012. We'd recently upgraded TFS, so I assume that was when/how my workspace got screwed up.
Can confirm that the TFS workspace nuke-it-from-orbit procedure fixed it for me:
- Manually delete all files on the development machine under the problematic project that can be deleted manually
- Right-click on the project and Get Specific Version (VS2012 moved this to Advanced > Get Specific Version)
- Make sure both Overwrite check-boxes are checked
Some of that is clearly unnecessary, but it's a bit of feel-better voodoo.