error: couldn't repair the partition map because a new EFI system partition couldnt be created

Time machine reported an error and couldn't back up, so I ran disk utility on the time machine drive and got this message.

"error: couldn't repair the partition map because a new EFI system partition couldnt be created."

Then I hit verify disk and got the message

"Error: partition map check failed because no slices were found."

Help?