From the Grub Documentation Page:
Invalid or unsupported executable format
This error is returned if the kernel image being loaded is not recognized as Multiboot or one of the supported native formats (Linux zImage or bzImage, FreeBSD, or NetBSD
Fedora doesn't do well at detecting or making entries for other OS's in the grub.conf (menu.lst) file. You need to make a manual entry. I assume you are able to boot Fedora? If so, just mount Ubuntu in Fedora and go to the Ubuntu /boot/grub/menu.lst file and copy the Ubuntu entry from there to /boot/grub/grub.conf in Fedora. If you don't know how to do this, post again. Also, it would be useful to post the output of 'fdisk -l' (lower case letter L).
Do you have two boot partitions on your drive (hda9 and hda12)??
Last edited by yancek; 10-04-2008 at 11:10 PM.