yeah well, I had this twice but I've been disconected form Drawchat but when I attempted to log back in it said username already taken? I logged in on my brothers profile and It still had my user name in one of the drawchat rooms...this is really annoying...
Some network connections that use complex routers or if you have an internet connection that changes IP addresses, you may get disconnected from DrawChat and have to wait up to 30 minutes before your previous connection is disconnected from our server. When this happens you will see a "username taken" message for up to 30 minutes. You will be able to connect again within 30 minutes time.
Unfortunately there is no answer to this right now other than just waiting.