Have you ever wonder what ‘The client version does not match the server version. You can only connect to a server with a matching version.’ error message really means? Since the error message shows the file (build) versions of the client and server it has been speculated that only clients and servers of the same build can connect, which is not the case. What really happens is that we have a communication interface between Microsoft Dynamics NAV Server and clients that has an internal version number which we change when this contract is broken (interface is changed so that it is not compatible anymore), and in that case the versions will not match and you will receive this error.