Problem is solved now ( but I must admit that I donīt know exactly why... )
I ran the hardwaretests and got an "MIDI-error" ( reason : I forgot a MIDI-lppo-cable between MIDI-In and -Out, thanks to AJ for this hint )
The I re-installed my OS 5.2a and now it works as it should do...
( I re-installed it beforr but nothing changed )
Anyway, itīs working now