What happens if you don't open windows (VM?) I think that you're virtual program is taking ownership of the usb port and that is why, it's not showing up on your mac desktop.
Unplug the pocketbook ( usb plug from the imac)... reboot your Mac.. ( don't open VM) then plug the usb cord into the imac and see if that works.
Also, do you have it plugged into a hub? Or in the back of the imac? If it's a hub... I have had problems with things plugged into an unpowered hub, not showing up or working correctly. They tend to work fine with a powered hub, though.
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