Comment 14 for bug 1091477

I solved my case today, thanks to your comments too.
On my HP Sleekbook 15, the EFI partition was read only because there were errors on it. Therefore it was impossible to make any change to it.

I found out the files under the "EFI/ubuntu" directory were totally garbled, the names themselves were random characters.

"EFI/ubuntu" was the only directory with errors, so it looks like the grub instance made the mess during the setup! That's why after the first install tentative the EFI partition can only be mounted as read only. No need to format it or make another one, just fsck!

This is how I solved the issue running Ubuntu from DVD or USB:

dosfsck -a /dev/"efipartition" #to fix the efipartition, remove ubuntu dir if necessary
sudo mkdir /boot/efi
sudo mount /dev/"efipartition" /boot/efi
cd /boot/efi/EFI/
rm -R ubuntu #if it's still there you must remove it
boot-repair #must be installed first

After that, Ubuntu started to be available as a EFI option, even though it was not the default one. But that's a different problem...
I hope this helps!