Well if there is no message in the logs maybe you can try to use the parameter jmx.remote.x.check.stub when lauching JConsole. (-J-Djmx.remote.x.check.stub=true)
(it is a not documented parameter I found in openjdk and that is working with the Sun JDK I used)
You need javax.management.remote.rmi.level to be set to FINER also.
You should have specific messages logs about tests made on the stub used for managing the remote connection. You should see where is the problem : the stub or the connection.
Bye
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