How to usb boot from Grub2 in Cdrom

[buynnnmmm1]

I use a Computer which cannot boot from usb memory.

I would like to boot usb memory with Grub2 in CD-RW.

I entered following commands.

insmod uhci

Then usb memory was detected with (usb0). 

I checked it with ls command. 

Then I would like to boot with chainloader.

set root=(usb0)
chainloader +1

But I got following error message.


Hard Disk Error
Insert system disk in drive.
Press any key when ready....


I can boot the usb memory with  "Plop Boot Manager".

I would like to boot with Grub2 without Plop Boot Manager.

(The usb memory was installed Ubuntu Linux. That can boot. I checked it with 
qemu.)

Please teach me how can I do it.