Thanks for your quick response Jim.
UAC is disabled.
I tried the uninstall including registry and library files earlier today, rebooting and reinstalling as the crash window suggests. The problem was still there.
However, I just uninstalled again and noticed the uninstall was done too quick (I confirm and it was supposedly done). The application folder (C:\Program Files (x86)\J River\Media Center 12) and User folder (C:\Users\Ingemar\AppData\Roaming\J River) were not deleted so I deleted them manually before rebooting. I then reinstalled and it seems to be working again, but I also noticed that all my registry had not been removed either (settings were still in place).
So it looks to me like the uninstall for MC12 in Vista is not working properly. Files and registry settings remain in place, or at least a large portion of it.
If there is anything you want me try out Let me know and I'll give it a shot.
Thanks,
Ingemar.