boot with grub on usb memory stick

[K. Posern]

Hi.

I am trying to boot from the USB "traveling disk 2.0" (usb 2.0 key) on an 
thinkpad X31 subnotebook.

I installed grub (GNU GRUB 0.93) on the USB stick.

The BIOS of the IBM thinkpad recognizes the USB stick as a harddisk ("Generic 
USB disk" appears under "harddiscs" in the boot order menue).

GRUB gets loaded from the MBR of the USB stick (stage 1 and 1_5  - I suppose)

BUT then grub breaks with ERROR 21 (during the loading of stage 2  - I suppose)

The following text appears on the screen:

_________________________________________________________________________
    GRUB Loading stage1.5.


    GRUB loading, please wait...
    Error 21
    <BLINKING-UNDERSCORE-CURSOR>
_________________________________________________________________________

Any idea, any hints for me?   (would be great ;-) 


Greetings,

Knuth Posern.