You may wish to check the port status monitor on the UC 1.2 server... it's possible some of the voicemail ports may have become locked up. It might also be worth checking the compatibility with the various versions of CUCM and upgrading to TSP version 8.3(1) if you haven't already. Have you tried rebooting the UC 1.2 server?
Please keep in mind that Unity Connection 1.2 is now a very old product and will no longer even be supported from March next year.
Kind regards,
Craig