Beach Comber,
In an earlier post, you mention that you have to have dedicated GPIB controller for this instrument. Is that still the case? If so, then the instrument is not only not comliant with 488.2, it's not compliant with 488.1 or any other GPIB standard and the problem might be with the instrument itself. Instead of VISA, you might want to experiment with the low level GPIB functions. There is the GPIB Clear and GPIB Initialization that you can try calling periodically to see if they make a difference. Performing a GPIB Status could also give you a clue as to what might be happening. If the instrument as an error query, you could also try calling that after every write to see if there is something it's reporting.
