What version of Armory are you using? The current latest version of 0.95.1. In general, you should use the latest versions; Armory 0.95.1 and Bitcoin Core 0.13.2.
I tried 0.95.1 and 0.95 with Bitcoin Core 0.13.2, 0.11.1, etc. Always there is some problem... For example, with latest Ubuntu, latest bitcoin Core I remember I had the RPC issue. I solved it by unchecking "Let armory run bitcoind" but after that then I had the issue of Armory taking 2h always to get online... and when it was online was showing wrong balance. Also tried older Armory versions like 0.93. In this case armory was always crashing just after finishing scanning blockchain. After a lot of debugging I give up... just want to know somebody who has Armory running on ubuntu to say his versions so I can make same setup.