device descriptor read/64, error -71
is the one to pay attention to. Looks like the device's partition table is unreadable. Assuming you've already tried rebooting - Have you tried the disks on other computers? Does this computer have more usb ports that you can try them on?
If the disk is ok it could be the port going bad, i.e. losing power. I've gotten the same error with a WD Passport because my laptop's USB ports couldn't provide enough power so I had to use an AC powered usb hub.
It could also be a bug in the kernel. With several kernels in the 2.6.2x series I've had the same problem after swapping disks in the same usb port. A reboot would always fix that.
Hope this helps