I'm running ZD 2 beta 2 but I had the same problem with beta 1. I thought that the new beta would fix it but no change.
When running ZD I get the screen saying loading but I never get to the main window. I'm running on Win 7 64 bit against a 6.0.3 FOSS server. It seems I'm getting all my 5 gigs worth of mail data as the store folder is about that size. I'm not sure where to start troubleshooting this..