for MySQL 5.5 errors occur when trying to lock the performance_schema (like information_schema). The default for CONFIG_db_exclude should be
CONFIG_db_exclude=( 'information_schema' 'performance_schema' )
automysqlbackup throws errors out of the box with mysql 5.5.X; this took me a while to figure out ( the above fix works ). Hopefully is a quick change.
The above fix works for me too, using the homebrew package.