Make sure the path to the ubuntu.xpm.gz (assuming you got that one) is correct.

From a command line(as root, or using su): grub
Then at the grub prompt: cat (hd0
and press tab to find the partition that matches where /boot is then keep using autocompletion until you have the path checked (for example "(hd0,6)/grub/splash.xpm.gz" for me).