You should give more information, like exactly what commands you send to reach that point. Since I assume your session doesn't last too long you might just as well send the exact commands sent to the server.
And the command to establish the sessions? Do you run any commands whatsoever before sending the MYLISTSTATS command? If so you should include them and their response so it's possible to do exactly the same as you do. (can of course censor the password. )
Seriously, this could be caused by anything between your account having something the udp api dev didn't expect to you running command X, Y then Z before MYLISTSTATS causing it. So include more details.