Please make sure to set your correct ip on the following;
login_athena.conf, map_athena.conf, char_athena.conf
// Character Server IP
// The map server connects to the character server using this IP address.
// NOTE: This is useful when you are running behind a firewall or are on
// a machine with multiple interfaces.
char_ip: <YOUR LAN-IP HERE>
// The map server listens on the interface with this IP address.
// NOTE: This allows you to run multiple servers on multiple interfaces
// while using the same ports for each server.
bind_ip: <YOUR LAN-IP HERE>
// Character Server Port
char_port: 6121
// Map Server IP
// The IP address which clients will use to connect.
// Set this to what your server's public IP address is.
map_ip: <YOUR WAN-IP HERE>
And make sure your inter_athena.conf are match on your MySQL credentials and database.
And change use_sql_db if you are using sql.
//Use SQL item_db, mob_db and mob_skill_db for the map server
use_sql_db: no
Also if you are using a different client and make changes on MMO.h make sure you recompile.