http://support.microsoft.com/kb/969271
Try these steps to fix the problem:
1. Open Visual Studio 2008.
2. Open the local copy of the solution file using File > Open Project/Solution. (Note that no source control glyphs are visible.)
3. Choose the File -> Source Control menu in Visual Studio, and the "Go online" menu item. The source control glyphs now appeared.
4. Choose File> Source Control> Change Source Control and make sure the binds are correct. Unbind and rebind if they are not pointing to the TFS server.
5. Check out a file, modified it, and checked it back in to source control.
6. Exit Visual Studio and restart. (This time Visual Studio connect to Team Foundation Server automatically.)
7. Open the local copy of the solution file. The solution should be under source control now
