3.0 is not backwards compatible with 2.3. Please wait until your server has been upgraded to 3.0 before you download / install the 3.0 client.
If a 2.3 client connects to a 3.0 server it will receive an error message saying that the server has been upgraded to 3.0.0. This is a good time to download and install the 3.0 client.
If a 3.0 client tries to connect to a 2.3 server it will just sit there saying "MSG: Contacting server".
Again, if you are not the owner of the server then you should wait until you get the error message from your 2.3 client.
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Edit-1: I have posted a preliminary version of the
UAR page here. Please read it to help you understand the new paradigm. It's not really hard. Just a different way of thinking and the only real way to control trouble makers, not to mention the voice and commanding targets depend on it.