Are you able to boot? That is, do you just see that message and otherwise everything's OK? If so, I'd just leave it be; it's a minor issue, and debugging GRUB problems (especially on an EFI system) can cause you to lose half your hair.
If you're not able to boot, then you may want to boot with an emergency disc and run the Boot Info Script.
This collects a bunch of data on your partitions, filesystems, and boot loaders, and stores it all in a file called RESULTS.txt. Post that file here (between code tags or as a download link) and those of us who understand such things can peruse it and tell you what we think.
More broadly speaking, the directory name /grub/i386-pc suggests a BIOS/legacy-mode install. If you're running on a UEFI-based PC, though, there's a good chance that you'd be better off with an EFI-mode boot loader. You can change boot loaders after the fact, so you needn't re-install to change, but you might want to begin investigating this issue. Consult my EFI boot loaders
site for information on the available EFI boot loaders, how to install them, and how to determine which boot mode you're using.
One more point: If you installed a 32-bit version of Ubuntu, it only supports BIOS/legacy-mode boots. There are ways around this restriction, but it's better to install a 64-bit version of Ubuntu, if possible.