max_allowed_packet is set in mysql config (my.cnf), NOT ON php side (ie. php.ini)
sql> SHOW VARIABLES LIKE 'max_allowed_packet';
In your my.cnf file, increase the size of max_allowed_packet to say 32MB (or greater than waht your database's settings are)
restart your mysql services and try again
PS. You don't really need 32M ... 16M should be fine too..