Did you try turning it off and on again? I mean, the full SAN shutdown/startup: http://support.apple.com/kb/HT4027
You're probably seeing "duplicate LUN labels" because the MDC has seen two LUNs with the same label but different serial numbers since it has been online. The serial number (which I think is based off the WWN) would have changed when the RAID controller changed. A reboot should fix that specific error message.
If the volume still doesn't start after rebooting, then you would want to check the cvlog for that volume.
What I eventually got to fix the problem was to go into the RAID admin and had to repair LUN Mapping for that side. It took just a few minuets and seemed to fix the issue of not mounting the volume. I still have duplicate LUN reports but it is not causing any problems with the volumes and persists even with a full system hard reset.