If you go to check a file out from Team Foundation Server, and get the error message:
The item <Filename> could not be found in your workspace.
First check the actual files on your computer to see if it's there. If the file is there, then you may need to recreate the workspace. Make sure you check in all pending changes that you want to keep first, because removing the workspace removes any changes you have waiting.
From the Source Control Explorer, go to the Manage Workspaces dialog, remove the offending workspace and then add a new one (you can point it to the same location as the old one). I then do a Get Specific Version on the tree, ticking the two options at the bottom of the Get dialog.