Hello Gandy,
I would like to know the following information:
-What is your CVI Version?
-What is your IVI Compliance Package Version?
-What is your VISA Version?
Also, I assume that you are trying to make your own instrument driver and not one for the HP34401A DMM. If you do need an instrument driver for this specific DMM, you can get it at www.ni.com/idnet.
If you have the latest versions of all these pieces of software, could you get me an NI-Spy capture of this failing?
Scott B.
Applications Engineer
National Instruments