[exim] mysql not working

I'm just setting up a new server, same OS (FreeBSD 6.2), same version of
Exim, (exim-mysql-4.68) - oddly my test are showing that exim is not
looking up with mysql at all. I've confirmed I'm using a username and
password that can connect using the the details from below from the config
file:

hide mysql_servers = localhost/database/username/password

Is there something that I've missed to turn on somewhere?

Thanks