Thanks AposMus for the tip,
Yes I tried the onLoadIntoSlot and the result is the same unfortunately 
The onInit doesn’t work and gives an error message 'No matching overload found, candidates: init setProgram(…). I guess, onInit needs a program that is already set into a slot.
I hope someone at Steinberg could give me a clue, so I can continue to move on? Please steiny I’m out of ideas 