Comment 9 for bug 733836

Exact same problem after an upgrade from 12.04 to 12.10.
I was having 3 "Error: file not found" when booting, but it was booting anyway.
After upgrading to 13.04 I had the same 3 errors + "Press any key to continue ..."

And the problem's resolved with Oliver suggestion: run "grub-install" .
Same symptom also, /boot/grub was populated with lots of ".mod" files and few remain after re-running grub-install.