Create an EFI partition

Googling the error message I get a plethora of different causes: e.g. no space on the main volume, broken SATA cables etc.

So restoring or rebuilding the EFI partition probably won't solve your problem.

Recreating a/the EFI partition should be easy though:

• Create some OS X installer thumb drive
• Detach your external drive
• Boot to the thumb drive.
• Open Terminal in the menubar > Utilities
• Enter diskutil list to get the disk identifier of your internal disk (probably disk0) - you will get about 12-14 disks almost all of them related to the thumb drive. Check the sizes to get the right one - below I assume it's disk0.
• Unmount disk0 with diskutil umountDisk disk0

• Check partition table:

  gpt show -r /dev/disk0
  

• Remove the two existing partitions:

  gpt remove -i 1 /dev/disk0
  gpt remove -i 2 /dev/disk0
  

• Create a new partition and re-add the other two:

  gpt add -i 1 -b 40 -s 409600 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B /dev/disk0
  gpt add -i 3 -b 1952255592 -s 1269536 -t 426F6F74-0000-11AA-AA11-00306543ECAC /dev/disk0
  gpt add -i 2 -b 409640 -s 1951845952 -t 48465300-0000-11AA-AA11-00306543ECAC /dev/disk0
  

• If the disk is stubborn destroy the gpt and a add a new one:

  gpt destroy /dev/disk0
  gpt create -f /dev/disk0
  

  Now repeat the previous step and add the three partitions.

• Attach the external drive
• Get the disk identifier of the external drive with diskutil list (probably disk14 or even higher - below I assume it's disk14)
• Unmount disk0 with diskutil umountDisk disk0
• Unmount disk14 with diskutil umountDisk disk14

• Clone the EFI partition of the external drive to your internal drvie with:

  dd if=/dev/disk14s1 of=/dev/disk0s1 bs=1m
  

• Enter reboot to reboot your Mac