I'm getting that message as well, but for me its on coins that don't quite equate to Bittrex's minimum order size.
for me on a few of my pairs I have less than a total of .00050000 BTC
for example, i have 0.02034704 LSK
trying to sell it at ~0.0015 BTC only comes out to 0.00003097 BTC
Thats my guess so far as to what that message means!