You may do better posting in the SLES rather than SLED forum

I can't try recreating this issue as I don't have a SLES install with any sort of graphical environment installed, but I wonder is this will help:
The page says it applies to SLES and SLED but I've never seen a root password prompt for mounting USB media in SLED. This post by says that in SLES only root can mount USB devices and it's Malcolm saying it so I believe it

Maybe mounting the drive manually would help.
$ mkdir /media/foo
$ mount /dev/whatever /media/foo
The value of whatever can be found by looking at the output of dmesg after you attach the USB device. E.g. If dmesg says the device has been allocated /dev/sdd then replace whatever with sdd1 to mount the first partition.