I couldn’t connect to TFS this morning. No-one else was having problems, just me. Restarting Visual Studio had no effect. Rebooting had no effect. I was about to Remote Desktop into the TFS server to see if I’d lost some permissions somewhere when the solution occurred to me.
I’d been recording some scripts for load testing, and to do so I’d set an http proxy in my Internet Explorer settings. Team Explorer apparently uses that proxy setting, too. Since the recording proxy wasn’t running, Team Explorer couldn’t connect to TFS.