Get rid of that that zombie build
Whilst upgrading a TFS 2010 server to 2012 I had a problem that a build was showing in the queue as active after the upgrade. This build was queued in January, 10 months ago, so should have finished a long long time ago. This build had the effect that it blocked any newly queued builds, but the old build did not appear to be running on any agent – a zombie build. ...