The following two rules gleaned from a post by Paul M on 2007-11-06 14:30:34 to the pfSense support mailing list.

7. Verify that ONLY the master sync server has the various sync buttons checked.
7.5 And just to be safe remove any IP address in the Sync form on the slave servers.

Make sure you have a rule allowing pfSync in the master firewall that works for and syncs to the slave firewalls

pfSense-1.2.1-VM does not appear to require #1. Just make sure they are the same between all nodes.