MySQL 5.5 not starting after master-master configuration
What's the exact version of 5.5 you're running.  If you're running 5.5.24 you might be running into this bug https://bugs.launchpad.net/percona-server/+bug/1008278.

If you are running 5.5.24 ensure userstat=OFF.  Really though this is annoying so you might look at just upgrading beyond that.