Team Foundation Server does not exist or is not accessible at this time.
Technical information (for administrator):
The underlying connection was closed: A connection that was expected to be kept alive was closed by the server.

This occurs because the web service calls to TFS are being interfered with by Fiddler (oh the irony). Fortunately the fix is very simple.

Just open up Internet Options, go to LAN settings and click Advanced under your proxy settings. Then add an exception for your TFS server, including the port name

tfs01.dev.geek.nz:8080 (assuming you use the default TFS port)

This will stop your TFS traffic from being routed through Fiddler (Fiddler captures traffic by acting as a proxy).