menchar,
You are able to read the iberr to determine the error that you are receiving. Error Variable (iberr) is the GPIB error variable. If a call failed with an error, the ERR bit is set in ibsta. The iberr value describes the GPIB error that occurred.
For more information about the iberr and the error values, please reference the NI-488.2 Help, which is found at Start >> All Programs >> National Instruments >> NI-488.2 >> NI-488.2 Help.
Hope you have a great day.
Sarah S.
Applications Engineering
National Instruments