Sorry for the late reply.
Both outputs now have an offset of plus 0.68 Volts , doesn't matter if I connect the Power-Supply or not and no matter what . Measured with a DMM at AO 0 and AO 1.
I see this voltage when setting the voltage with LJlogger, too. I even see it while booting up the PC, before windows has started properly.
The AOs of a second U12 I am using are working in a correct way.
The Offset is not completely linear:
Voltage set in Software/Voltage measured
1V / 1.6V
2V / 2.4V
3V / 3.3V
4V / 4.15V
5V / 5V
I had an additional trouble, don't know if they are a possible reason for this behavior: I am using two U12 parallel, with a multi-thread-application. One day, the first U12 didn't start properly anymore. The green LED blinks some time then is switched off to start to blink again. The second U12 had the same trouble some beginning some days later. Resetting the Watchdog by wire and restarting it with the software removed this problem, but I'm not able to recalibrate the AIs.