It might be easier to check with fw guys if they see traffic blocked.  Bare in mind that this error can happen under different circumstances.  For example, when using wizard for add DD devices, you must make sure that all boxes involved (server, storage node, NMC and DD) can communicate with each other over VLAN on which devices or DD is being defined.  Some folks miss that when adding devices as they assume server and DD should be enough assuming NMC doesn't need to be as it would push commands over server, but that is not the case.