“Sorensen Error Query.vi”, code -1074003951

I am a complete novice to LabVIEW, I have a couple of Sorensen DLM power supplies that are controlled by GPIB.  These get errors like“Sorensen Error Query.vi”, code -1074003951 and VISA Write in Sorensen Read voltage output.vi->PDFT 150V RevA1.vi.  I am trying to figure out if this is a hardware or software issue, then how to fix if it is a software issue.

Sometimes the program runs for 8 hours without error sometimes 30+, but need it to run without faulting for a longer time.

Thanks for any input,

MKroll