The refnum class cannot be defined because a class has not been set or because one or more external files that are used to define the refnum are missing.

To correct this error, set a class on the refnum or install the driver associated with the refnum. The driver contains the external files that are needed for defining the refnum. If you have moved the external files, move them back to their original location, close LabVIEW, and restart LabVIEW.