(Just in case anyone else runs into this situation)

I set up RTS (1.4.4.42095) to connect to a number of servers.  Connections were successful for some, but for others I received the following error:

System.ArgumentException: Value does not fall within the expected range....

This came from GetServer.  I went into the server info editor, placed my cursor at the end of the server name and hit the Delete key a few times, then saved the server info.  I could then connect.  It seems there were some non-printable characters in the server name that couldn't be handled.