Disconnect from Server when clicking in GUI (SC 18.92, Forge 14.23.1.2555)

[March75]

With following Message on the server:
07:48:01 CONSOLE: Epoll Server IO #5/ERROR] [FML]: FMLIndexedMessageCodec exception caught
07:48:01 CONSOLE: Undefined message for discriminator 5 in channel rebornCore
07:48:01 CONSOLE: java.lang.NullPointerException: Undefined message for discriminator 5 in channel rebornCore
07:48:01 CONSOLE: Epoll Server IO #5/ERROR] [FML]: SimpleChannelHandlerWrapper exception
07:48:01 CONSOLE: Undefined message for discriminator 5 in channel rebornCore
07:48:02 CONSOLE: java.lang.NullPointerException: Undefined message for discriminator 5 in channel rebornCore
07:48:02 CONSOLE: Epoll Server IO #5/ERROR] [FML]: There was a critical exception handling a packet on channel rebornCore
07:48:02 CONSOLE: Undefined message for discriminator 5 in channel rebornCore
07:48:03 CONSOLE: java.lang.NullPointerException: Undefined message for discriminator 5 in channel rebornCore
07:48:03 CONSOLE: Epoll Server IO #5/ERROR] [FML]: Network Disconnect: A fatal error has occurred, this connection is terminated

[modmuss50]

Can you post the full log please?