One thing you might try is to just go ahead and mount it manually. Knoppix never recognized my USB thumbdrives. I always had to add them manually.
Do:
mkdir /mnt/usb_external
mount -t vfat /dev/uba1 /mnt/usb_external
note: you may need to substitute ntfs for vfat if your external is formatted with ntfs. It's not supposed to be but you never know.
let us know if that works.