Worked for me, cheers! (I had problems in Mozilla so used IE9)
I ran into the exact same issue when configuring WAS 6.0.2, WCS 6.0, MQ 6.0, etc... I will not claim this will resolve everyones issues, but in my case a simple restart of the server was in order, and the MDB started up ok, with the listener port started.
I think it may have something to do with the fact that the "default mode = started" was choosen, but it had not been started yet. But do not quote me on that!
I hope this info helps someone who finds themself in the same situation.