A quick Google search came up with this "When players get this error it can be for various reasons, but most commonly they are: A recent Assetto Corsa update has not been applied to either the client or server. As such the files on the client and server don't match. Some (add-on) content on the server is not the same as on the client." I connected OK 10 mins ago, so our server is up to date.
Sorry to hear you can't make it to most of the races Kimi . Please remember to unregister from any that you won't be attending.