And which line is the error on? I'm guessing you have a null ref exception there. Add some null checks for your code.
In your OnNetworkJoinChannel you seem to be calling JoinRandomChannel, and then proceed to use chatScript. Does chatScript even exist? I'm guessing you want to wait until you get "success == true" before doing anything. JoinChannel is a delayed call. You shouldn't do anything after calling it.
To send audio data, send its bytes. You can't send the clip.