I have an external, self-powered HDD, and when I plug it into the front USB port of the computer, it doesn't mount - instead, I see:
new high speed USB device using ehci_hcd and address 15 configuration #1 chosen from 1 choice USB disconnect, address 15
It works fine when it's plugged into the USB ports at the back of the machine (which are right on the MB). Other devices - usb keys, my cameras, etc - work fine in the front ports.
Does anyone have an explanation for this? Could it be power related?