Hi Stefatronic,
there is definitely no problem with your licensing. I have Power Pro Edition and also get 2.5V on Channel B.
The problem in your circuit is, that your ground, which you have put between V2 and V3 with each 18V makes problems (short circuit?).
When you look at my modified file in the attachements you see, that you get almost -29V on Channel B.
So, i think, the problem is more caused by false wiring or/and false grounding.
If you want to build controllers this link may be helpful for you:
ftp://ftp.ni.com/pub/devzone/tut/6655_controllers_2.pdf
Abduelkerim
Abduelkerim
Sales
NI Germany