I recently ran into a situation while trying to migrate a project from SVN to TFS.
I used the Export command of Tortoise SVN to produce the output I would migrate. This effectively produces a "clean" copy of the code (no SVN folders).
When I tried to add the code to TFS via Visual Studio, I noticed the solution kept loading with SVN bindings (I use the ANKHSVN plugin). If I tried to switch the plugin, it would ask me to close the solution.
I went poking around in the Solution (.sln) file and found the following entry:
GlobalSection(SubversionScc) = preSolution
Svn-Managed = True
Manager = AnkhSVN - Subversion Support for Visual Studio
EndGlobalSection
Removing this "GlobalSection" did the trick for me. After launching the solution again, I was able to add it to TFS.
I hope this helps anyone with the same issue out there.