What version of UM are you running?, you can also try using Welcome in 15.10 and 16.04 which also has a couple of repair functions:
Do you have Synaptic installed?, open Synaptic and look for "grub and systemd" and right click both for re-installation, don't agree to run other updates, once done; restart your system and try updating again!.
I don't know if you are aware but please read this in case you didn't follow this advice!: