Pass a 'null' for the scene name when joining a channel.
Just note that loading a scene via an RFC is a bad idea. TNet manages lifetime of object creation and RFCs in a specific order, and newly joined players receive packets in a specific order. Loading the scene is always first, followed by creation calls, followed by RFCs.
If you make scenes load from RFCs, you effectively break this order as loading the scene won't be first anymore. Objects may not be in the correct state, and RFCs will be fired before your scene loads, likely causing issues.
It's a much better idea to pass 'null' when joining a channel if you know that all the objects in the scene are already present and none will be dynamically created, allowing you to use chat and such. When it's time to actually play the game though, TNManager.LoadLevel the proper game scene.
