Update :

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 wink
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Greetings from East-Frisia ( Northern-Germany )