This problem can occur if the client reuses the same socket and sends another stream to Hyves XMPP server.
The Hyves XMPP server only accepts connections once per socket/stream

The solution would be to use a new socket for every new stream. If a new socket is created then it would be possible to reuse the same resource.
It is strongly advised to NOT create multiple resources as it may result in unwanted behavior as it may cause problems with routing on the server.