I ran into this because my pass phrase had a "`" in it. When I went to assign my rewards I would constantly get unknown account , code 5. (something like that).
I chased it down to the encoding of the pass phrase from the html. Just need to change (burstcoin/html/ui/rewardassignment.html) to have this at the top:
I am looking to do a pull request for the changes, but until then you can modify your own HTML and get around that problem.