Ubuntu 16.04: grub-efi-amd64-signed failed to install into /target/ error [duplicate]

Solution 1:

The EFI System Partition was corrupt. I rectified this error with the following steps:

On Windows, I used DISKPART to assign the EFI System partition a letter. Fired up DISKPART, and typed LIST DISK to find the disk, followed by SELECT DISK <N> (where is the drive number). Followed the same steps to find the proper partition (i.e. LIST PARTITION followed by SELECT PARTITION <N>), and then simply typed ASSIGN LETTER = X to have Windows mount the partition to letter X.

Then opened CMD with administrative access. Ran CHKDSK X: /f /r

Then, I tried installing Ubuntu once again, and it installed successfully!