partitioning - Ubuntu Dual boot with Win 8.1 help!

Total newbie here. I want to install Ubuntu 14.04.3 alongside Win 8.1 that's already there. I'm getting the same error no matter what - "The attempt to mount a file system with type vfat in SCSI1 (0,0,0), partition #1 (sda) at /boot/efi failed.
I tried all of the following:

1. Selected "install ubuntu alongside windows..." - result is that
   installation stalls.


2. Selected "something else" and tried creating 3 manual partitions:
   ~45GB for root ("/") as ext4, ~17GB for swap, ~30GB as ext4 for
   "/home". Result - the above error message.


3. Somebody had suggested partitioning using GParted and then running
   installer.. Tried this too, but GParted doesn't let me partition as
   "Logical".. I only see "primary".. But, even then in GParted, I
   don't see an option to set "/" or "/home" etc.. So I got to do this
   
   in the installer? If yes, then what's the point in partitioning
   beforehand?

Any help is greatly appreciated! Thanks!