I was hitting this exact error message during installation. I switched to another VT and did:
mkfs.fat /dev/sda1 Then I switched back to the installer VT, and had it try again from "finalize the partition layout". Now it's proceeding with no error. I took the idea from this Ubuntu discussion: https://askubuntu.com/questions/502307/ It looks to me like the installer doesn't ensure the EFI partition contains a filesystem before trying to mount it. -- Aaron Bugher
