So here's an obscure one. I was getting the post's title as an error when trying to install the Scrum for Team System template on a new TFS 2008 server.

I tracked it down to the fact that this particular TFS server has multiple IP addresses, and I had set up the default web site (where I was letting the Scrum template install its services) set to one of those IP (the one our DNS points the TFS2008 FGDN at). Temporarily setting this back to All Unassigned (and juggling a few port numbers on other sites around to allow me to do this) fixed the problem. It has something to with with how the MSI installer was trying to create the new virtual directory in the Default Web Site.