Hi Fischer,
The most common cause of this error is having an incorrect Instrument Descriptor. Is your DMM locally or on a remote PXI system? Please check the following:
http://digital.ni.com/public.nsf/websearch/22CF7E6B27B6995B86256DDB0058F39B?OpenDocument
Is it possible to use the DMM from LabVIEW, CVI or any other development envirnoment?
Let me know if you have success with that.
regards,
Nikolai