TF400324: Team Foundation services are not available from server…

Quick Fix

As a quick fix you can

1. Close Visual Studio and related apps
2. Browse to %LocalAppData%\Microsoft\Team Foundation\4.0\Cache and delete all the contents of that folder

This isn’t ideal as you will need to do this for each client and every time you switch between the 2.

Better Fix

As a better and more user friendly fix, you can

1. Do the Quick Fix
2. TS to the server where you have The new TFS server with a copy of your collection attached (my TFS 2013 instance)
3. Open a command line window in Administrator mode
4. Run cd C:\Program Files\Microsoft Team Foundation Server 12.0\Tools”
5. Run tfsconfig ChangeServerID /sqlinstance:<Your Sql Instance Name> /databasename:<Your configuration Database Name> /ProjectCollectionsOnly
6. This should bring up a message that says “The command ChangeServerId should only be run against a set of Team Foundation Server databases that have no application tiers configured. Do you want to continue with this operation? (Yes/No)”
7. Type Yes and hit enter

Now you should be fine to use both instances of TFS with the same collection name without issues