Telepathy is not yet available here at our company, but we're practicing...
Sorry for the irony, but honestly it's unlikely that we can help by just seeing a few lines of code of your joinRoom handler

The problems is likely to be generated by what was done before.
Now, before you post all your code and ask for a code review please take some time with our documentation which already provides clear examples on how to implement a custom login.
Here are tutorials that will help:
http://www.smartfoxserver.com/docs/docP ... /index.htm
http://www.smartfoxserver.com/docs/docP ... /index.htm
Additionally please check the AS3 API documentation. If you check the docs for the onJoinRoom you will notice that the room is already passed to you in the event.