I also had to ditch my old VM when I went from a beta version to the "regular" version of VPC on windows 7. Got to say that this was NOT friendly at all of this software, but then in my case as I was going from beta to full release software, I'm not really surprised by that.
You'd have thought that there would be some kind of migration path from older version of VPC to the latest - other than copying everything to DVD first!
Oh well.