At first i want to say "thank you!" for your replies.
The writer is working again, i re-flashed it with A104. (but i'm still confused with this B/D stuff
The problem seems to be my attempt to flash with the usb cable.
Though everything seemed to work fine (no errors reported) the troubles
started after the reboot. (i tried flashing A105, A104, A103, all with the usb 2.0 port)
Before taking the drive back to the shop i made a last attempt using the Firewire port
After flashing A104 this way the drive works again. I'm happy now and don't
dare to flash A105. Maybe i will try A106 if it should appear someday...
Again, thanks for your help!