Here We Go With Ground Loops Again

Got the latest version of the Allen Bradley PanelView 1000 plus, (the new "C" version) and it is exhibiting a peculiar trait. Plug in a memory stick to the USB port, and the entire 24VDC system in the control panel is drug down so that other 24VDC devices turn off, until the fuse protecting the panel view opens. The PV is 24VDC powered from a Rhino power supply. The panel has 120VAC in it generated from 480VAC with a transformer. X2 on the 120V output side of the transformer is grounded to create a neutral. The PV is grounded to the same ground as all devices in the control panel as well as the transformer. The control panel and the door the PV is mounted in are connected to this ground. The last time this occured, I believe we managed to burn out the internal power supply for the USB port. (kept trying different grounding schemes to see if we eliminated the problem until we got fire and smoke - but the PV still functions) I called Rockwell support and they could only refer me to their knowledge base site and referenced a grounding tech note. This note concerns grounding of devices with external and seperate power supplies - not one contained in the PV. Other devices in the system that are 24VDC are relays and 4-20ma instrumentaion. One odd device exists on the 480VAC side - a water heater that functions by putting 14VDC at 800 amps directly across tubing that the process water flows through - one bus of this heater is connected to the common ground, per the designers wiring schematic. We know that when run in a test prior to installation in the control cabinet, the PV functioned normally and a memory stick could be inserted sans problems.