This morning my controller magically became visible. Also, I got an error regarding a very long SnapMirror transfer from a remote branch office which took several days to complete (with an error). Anyway, I think this might be related. Do you have some SnapMirror relationships set up, with that controller being a destination? if so, try quiescing them and see if that changes anything. Let me know!
Re: System Manager (OCSM) not loading volume information on ONE controller