This will happen to you if you’re trying to clone a project from TFS to create an identical project and then re-upload to TFS.
What will happen is that, if you change the file structure and go back into your code to correct the references, when you’ll try to check in TFS, all the projects should happily bind but the sln file will not be bind.
In that case, what you need to do is to open your .sln file in a text editor and locate the lines that read: “SccTeamFoundationServer =”
You will notice that not all of the references point to the correct target. You need to correct those URLs, save the file and try to check in again.