Remember, remember, remember…to close the TFS Administration Console!

That was fun :) While working with TFSConfig I hit this error on a TFS Farm’s Application Tier…

Oh, right, I have it open. I run the command again after closing the console and I get the same error.

The lesson? Close the TFS Admin Console on all the Application Tiers of your TFS Farm, otherwise TFSConfig will detect it as open and return an error.