Thx for the help, weight and balance sounds logic to me.
I started the figuration of the flight from scrap.
100% fuel eand changed nothing concerning the payload, all went ok.
then I changed teh payload exactly I did the first time, and believe it or not, all went ok, the aircraft remained on his feet.
eind goed al goed, we say in dutch.
Weird situation, but anyway, thx for the help.