Convertor not working some times

[promy]

I build a wiper motor 2-dof chair , like http://x-sim.de/forum/viewtopic.php?t=1617topic
However i'm having some problems setting it up.
The arduino works (manually sending values works).
I tried to setup math with the wizard (3 axis, but send only the left and right to the arduino.)
I thought it was working (a bit, not fluent yet), but for some reason it sometimes does not work (just no movement, it seems that nothing is getting to the convertor?

Any idea's what i'm doing wrong, or is there a tutorial i can follow?