Hi Mars-
It sounds like your NI-DAQ installation may have become corrupted. I would suggest uninstalling and reinstalling the DAQmx 7.4 driver to correct this problem and ensure that you're up to date. This download is available here:
NI-DAQ 7.4If the problem persists you may want to uninstall and reinstall LabVIEW and then NI-DAQ in that order. The error message will usually give an indication as to which VI the error occurred in. Please let us know which VI is failing if you're unable to avoid the error with these suggestions.
Have a good day-
Tom W
National Instruments