Hi Cyril,
I tried your suggestion, but no change. The problem appears to be when the window focus is not on the SystemExec window, USB communications bog down. The programming progression bar on the PM3 hesitates repeatedly. I tried RS-232 control of the PM3 programmer, parts programmed in ~5 sec with SystemExec.vi window min or max. Unfortunately, I won't have an open RS-232 port or PCI slot in the final application.
I'll take a look at the Windows API Function.
Thanks,
Darell