I have no idea if this is what caused the problem, but many older flashes have high-voltage trigger levels. This can wreak major havoc upon newer cameras that aren't robust enough to deal with it. You can buy special adapters and PC cords that have voltage filters in them.
If this was the problem, SunPak would be right: the flash is performing to spec, it's just that the camera can't deal with that spec. If you ask them, they can probably tell you what the voltage is and then the camera manufacturer can tell you if that is acceptable.
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