Usually, I copy the Application Data\ Folder\Camera Bits, Inc.\Photo Mechanic (without cache) from Win XP to Vista to have all snapshots etc..
I guess, this is the problem. After I deleted the AppData\Roaming\Camerra Bits, Inc folder on my Vista UserAccount, PM is working again.
Now I will copy more selectivly my settings from XP to Vista, until PM offers a opportunity for export of the settings.