Getting "error communication with USB Mass Storage device" when running ls (usb0) (or ls (usb0)/)

[Kevin Wilson]

Hi, grub gurus,

I have a CentOS release 6.2 machine with  GNU GRUB  version 2.02~beta2
I have a Kingston USB dongle plugged in into it
When I boot, I press "C" from the grub menu to start in console mode, and
I reach the grub prompt.
>From the grub prompt, I run ls, and I get:

(cbfsdisk) (proc) (ahci0) (ahci0,msdos2) (ahci0,msdos1) (usb0) (memdisk)

I can run (ahci0,msdos1) succesfully to read the
 /boot partition on the machine ( /boot is mounted on /dev/sdb1, its
type is ext4)

However, when I run ls (usb0) (or ls (usb0)/) I get:
error: error communication with USB Mass Storage device.
On the USB disk I have an ext4 partition (/dev/sda1), and I can mount
this USB partition
succesfully on the CentOs machine.

The "communication with USB Mass Storage device" appears in both
cases, when the USB dongle is mounter
and when it is not mounted.
Any idea what is the reason for this ?

Regards,
Kevin