Grub 1.98 does not detect USB drive

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I'm trying to boot a flash drive (pendrive) using Grub 1.98; so I've modified 
the configuration scripts with the following lines:

#!/bin/sh -e
echo "Prima prova"
cat << EOF
menuentry "linux-CF" {
search --fs-uuid --no-floppy --set=root 4e7b5e28-5275-45be-8f20-8ed4dd18666a
linux /boot/vmlinuz-2.6.35 root=/dev/disk/by-uuid/4e7b5e28-5275-45be-8f20-
8ed4dd18666a
}
EOF

"4e7b5e28-5275-45be-8f20-8ed4dd18666a" is the UUID USB device /dev/ubb1, 
obtained by blkid command.

I've installed the bootloader on the pendrive with the following command 
(dev/ubb1 mounted on /mnt/pendrive):

grub-install --root-directory=/mnt/pendrive /dev/ubb

So, I try to boot from pendrive, but the following message returns:

error: no such device: 4e7b5e28-5275-45be-8f20-8ed4dd18666a
entering rescue mode...
grub-rescue> _

It seems that Grub does not detect /dev/ubb1.

I ask you how I can solve this problem.

Thanks for reading this,

Filippo