Josh, this is from first.ptc.com which is the retired Windchill 9.1 server. Any particular reason you are still working on this server? This system should have been shut down last year and I am putting together a plan to fast-track its retirement and shutdown in July 2013.
All browsers or just a specific one? When is this error presented, at initial login or while accessing a particular object/page? I could not reproduce with IE, FF or Chrome. What OS?