There are a few small inputs due to receiving a couple blockchain.info shared sends a while back. The smallest being .005 and the majority much bigger than that.The amount I'm having trouble sending is very small in contrast to the amount of total spendable funds though.
Can you do me a favor: do whatever it is that triggers the error, then go look at the Bitcoin Core logs: /home//bitcoin/debug.log . As soon as you see the disconnect message in Armory, you'll see a message in the logfile telling you why the transaction was rejected. This is the most direct way to determine why it's failing.