Hi,
You'll have to clarify the problem. On one hand you talk about NI-DAQ, but you mention the NB-GPIB/TNT (not NBGRIB/TNT), which is not a DAQ card. It is also not clear where the error occurs. Does the error occur when you execute the program? or when you try to open the sub VI?. I suggest you redefine your question and post it on the appropriate discussion forum.
If you have a DAQ card, using the NI-DAQ driver, post your question on the Multifunction DAQ forum. If you have a NB-GPIB/TNT, you should be using the NI-488.2 driver and post you're question on the GPIB discussion forums.
DiegoF.