@ Richard: Eco acetone doesn't work. It has to be more pure, try a paint store or other specialist.
Edit: I see you're from the Netherlands, since a while the acetone in hardware stores etc. are the eco types. Probably a government thing. I bought some good acetone from ''werkenmetmerken'' online, good and relatively cheap in 5 liter cans from Bleko Chemie.
Ok, I will get the real(pure) stuff :) and try again.