My issue was related to my MySQL server having multiple network interfaces with one configured public and one private and these connection errors were a result of how I set up the mysql user. I had it set up as kamailio@'private.ip' but kamailio was actually attempting connection to the public IP (which was not authorized). If you have multiple network interfaces I would suggest checking kamailio.cfg and the user set up to access mysql and verify your IP's/hostnames and maybe even verify on both boxes what interfaces the connections our going out/coming in on.