Also make sure that you and your friend are using the exact same published version of the game. Even removing an unused variable or function will make the new script incompatible to the old one. If you need a different code on client and server, use anet_use_handles(0).

Also, you can try to load the server IP from a text file so you don't have to chance it in the code every time.
And might try to set a password. Its just that I've never tried using an empty string, maybe there's a bug.

EDIT: Still, dark_samurai is right. If the connection works locally, but not over the internet, its usually not ANets fault but your firewall/router. Do you have a firewall? If using the build in windows firewall, make sure it doesn't block the server.