How do I detach a project from ClearCase in order to add it to a TFS source control system?
Solution
I know it's silly but here's what I needed to do -
Open each of the csproj files
For each one, remove the xml nodes starting "Scc" (like SccProjectName, SccAuxPath, SccProvider etc) it seems they were the ones bothering the Visual Studio.
Reload the projects and add them to desired TFS workspace
Additional Steps that may need to be done:
Open the .sln with a texteditor and delete the entire section about source control.
In Visual Studio go to Extras -> Options... -> Sourcecontrol and change the plug in to TFS