Hello!
Usually I've found the answer with Google or from the forums or just being stubborn until I solve the problem but no such luck this time 
Anyway, we have a growing problem with our production because NI GPIB-USB-HS is giving EPWR (28) error and nothing seems to work. It's a random problem that occurs on ~20% of the test PCs. It could disappear for a while if we exchange the GPIB-USB-HS between two testers but the problem resurfaces somewhere else half a day later (we've got like ~25 GPIB-USB-HS's...)
Setup:
- We've got industrial PC's equipped with NI GPIB-USB-HS which is connected to a safety tester.
- During high voltage test we poll safety tester once in a second is it still testing ("STAT?").
- During the test we suddenly get EPWR (28) error and after that we need to disconnect the USB cable or remove GPIB-USB-HS -drivers in order to get things working again (otherwise we get EDVR error when trying to initialize GPIB board).
- We've got latest NI488.2 drivers (3.1.2) and VISA drivers (5.1, 5.4, 14.0, whatever is the correct version for "VISA").
- The power saving options are all set to disable. From Two places. (DOUBLE CHECKED!).
- PC's equipped with GPIB-PCI don't have this problem.
- EDIT: We're using Windows 7
Ps. Right. This wasn't a problem until we changed our code to poll whether safety tester was still testing or not.
Thanks
Janne Yli-Arvo, Testing Engineer
Vacon Plc, Finland