Mike - like a baud rate problem, that's what! I can run the same app'n on a PC already happily fitted with NI-488 serial-ports without intervening in settings and get clean data, but try it on PCs with conventional RS232 and it's mangled in a manner highly suggestive of baud-rate schism...(plus, writing-out from the port gives a framing error at the instrument end)
Shame: dispensing with NI488 had been vital to the project's success