Cannot convert 3.0 VM to 4.0 machine (Windows XP)

I have a problem here as well. I upgraded my Paralles Desktop 4.0 for MacOSX (german version). When starting I selected the 3.0 VM machine. Systems says i must backup and then convert my VM. The backup seems to be done sucessfull but when starting to convert the 3.0 VM to 4.0 I see a window for about 10 seconds, then i only see that blac spash screen and after 30 seconds or so i get a window with a "severe error".

I tried it several times but i cannot convert my VM. Fortunetly the backuped 3.0 VM backup is still usuable to startup with again downgraded Paralles Dektop 3.0

Hardware: MacMini 2.0GHz, 2 GB RAM, 120 GB harddrive, Bluetooth keyboard + MightyMouse. Software: latest OSX 10.5

I must hereby express my dissapointment with Parallel Desktop 4.0, 40 Euros wasted so far. I am sincerly considering to ask to get my money back because 4.0 is utterly useless for me.