The TFS add-in for Eclipse doesn't automatically check out files when you edit them, and you get this annoying and misleading error message when you go to save:
Mathematica could not write some data to the file C:\Dev\ProjectName\Main\Mathematica\ExcelImport.nb. You should check that file's permissions.
I've looked up a couple of threads:
http://team-foundation-server.blogspot.com.au/2007/06/automatic-checkouts-with-team-explorer.html
TEE 2012 does not check out files automatically
what's the best way to checkout from TFS to eclipse using TEE?
But in my case we're using it for Mathematica projects and they have the Team menu but they do not have the select Share, then select TFS
Hopefully someone out there knows a workaround, we are using Juno with TFS2010 (cough @EdwardThomson)
If you're using TFS 2012 you can create a local workspace rather then a server workspace.
Local workspaces work in a similar way to SVN and there is no need to check out files to edit them