if you're trying to sell maximum amount, remember to include the 0,19% fee on your calculation as it is removed from the original amount,not the amount you receive in trade.
for example.
if you sell 519 coxes
the actual amount to sell is 519/1,0019=~518.01577 coxes
hope this help if not,contact us on our irc support http://webchat.freenode.net/?channels=crycurexsupport and we will help solve the problem