I would make sure that the DET-MIIC-PRD server does not have another application running on the 50200 port; the PCO agent would typically throw an error and not start but just to sanity check this. I would also recommend that since you seem to be accessing a production PCo server from your Dev MII instance that your network security isn't blocking this data exchange, if there's a network switch involved controlling the traffic this will also strip data out.
Finally, since in the above you said the query was working when notifications where enabled from PCo to MII and then when you disabled the notifications they stopped working...is this still the case?
Perhaps we should have an SAP Connect to further troubleshoot this one out and then post our resolution to this (very long) thread.
Sam