For testing it is advisable to ensure that both client and server are running the same JVM version. The client and server are likely to operate correctly with mixed versions, but fixing on one reduces the chance of errors.

The default Repertoire Server port is 8080. If you have changed this, then you need to ensure the client connects on the modified port. Similarly, if you have configured the server in secure mode (the default is false), then clients connecting to the server must also connect in secure mode (usually over a different port).