The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
I refresh token is the token used to remember who you are logged in as. When does the error occur. It might happen in case that you were logged in while your token expired.
How did you get the error? Did you copy it from a pop up dialog or the log? Did you have any other problems?