[tsac]

I talked to a friend and he indicated the MAC can have issues with the USB ports . One problem known to all computers including MAC's is the use of a port that is on a hub and not a direct USB port. Most computers offer multiple USB ports but generally only one or two are direct and not hub ports. You can try different ports and see if that helps. I know on my computer only one port is direct and the 4 others are hubs but none are marked as direct so it's a try and see.