Hi Markus,
It sounds as though you are having problems with your PCI-6014. The difference in software versions shouldn't be an issue at all, so don't worry about that too much. If you try to output a voltage with the PCI-6014 and you are reading a voltage that is off by as much as half a volt depending on which voltage you choose, it definitely sounds like a problem with the actual card. This is backed up by the fact that you are reading that same voltage on the multimeter as well.
You can definitely test this by trying to replace the PCI-6014 with a different DAQ card to see if you get the same results. My guess is that you will see the correct readings on both sides if the card is replaced.
It sounds as though your board needs to be repaired or recalibrated. You can give us a call at 1-866-275-6964(866-ASK-MYNI) and we will be more than happy to get that set up for you. If you have any more questions or concerns, please feel free to post them in here and I will get back to you.
Regards,
Matthew Slaughter
Applications Engineer
National Instruments
LabVIEW Integration Engineer with experience in LabVIEW Real-Time, LabVIEW FPGA, DAQ, Machine Vision, as well as C/C++. CLAD, working on CLD and CLA.