I appears that you're going to have to update the old program to use the gpib functions in LabVIEW 5. I've seen this problem happen when an entire hierarchy was saved - including vi.lib files. If you do have an llb with older NI gpib functions in it, delete them from the llb and the next time you open the top level VI it should open the newer LabVIEW 5 gpib functions assuming that they're the same name.