Nevermind... figured it out. For some reason the new version of VirtualCenter doesn't like long .iso names (like the ones Microsoft uses if you have an EA or Technet account). I just renamed my .iso images to shorter names and everything is great. Though I still think this is a @#$@# thing to just "toss in" on an upgrade like this... especially since I now won't know what I've downloaded as matched against the official .iso names from Microsoft.