Can't unbind solution from Team Foundation Ser

I have some solutions that are binded to TFS 2010. But a team project collection isn't avaible any longer. I need to rebind this solutions to a new Team project Collection on this server. I tried to change Source Control (File -> Source Control -> Change Source Control). After pressing "Change Source Control" the window with the worlds "Would you like to completely disassociate solution from TFS" appeared, I pressed Yes. But when I'm trying to add this solution to this new project collection, I have the message that I cant do this, because the previous team project collection is unavailable. I've deleted tags from solution file and projects files and all *.vssscc, *.vspscc files. But I have got the similar error message after several attempts.

Message:

Team foundation server http://tfs.dynamics...etc does not exist or is not available at this moment. Technical information for the administrator: Service Team foundation not available on server http://tfs.dynamics.../<OLDPROJECTCOLLECTION>

Something is clearly remembering the old collection.

One option, if you still have access to it is to re-enable the old collection, unbind cleanly from it, and rebind to the new collection, before you decommission it. That way Visual Studio has the best chance of cleaning up or overwriting any references to the old collection before it is removed.

If it's too late, then places I'd look (in priority order) are:

Make sure you've removed the old collection/server from your 'connect to TFS server' dialogs
Make sure any workspaces for the old collection are deleted, and that the folders containing your solution/projects are mapped into the new collection's file structure. (Old mappings may prompt VS to add the bindings back in for the workspace it thinks applies to those folders)
Clear any references to the collection out from any solution and project files, and delete all the source control binding files (vssscc etc)
Search for in all files (.) in your source tree
Search for throughout your registry (proceed with extreme caution if you find anything and want to delete it)