When I boot up on SUSE 9.1 professional Linux box, I got
the error message "You passed an undefined mode number". If I hit the space bar or
do nothing for 30 seconds, the system will continue booting up, and my KDE window manager work just fine.

Is there a way to get rid of this annoying message. I searched the archive regarding this issue, telling me that I have to modify the file, lilo.config to fix this problem. However, with SUSE distribution, it use GRUBS, so there is no lilo.config to modify.

Any ideas?

Thanks for any help!

Edit /boot/grub/menu.lst and change the vga= option to a different number say 791 for 1024x768 resolution. Or remove that option entirely if you dont have support for it in your kernel.
Removeing that will just make the console screen 640x480 or something, probably what you see now when you boot.