Bukkit server - I can connect but no-one else can

Title sums it up nicely. This problem is odd though; I know it is not an issue with networking (so I've port forwarded correctly etc.) because I can run a vanilla server and everyone can connect fine. When I run my Tekkit Classic bukkit server though, I can connect via localhost but my friend gets "Failed to login; bad login" and my server log is

[INFO] /88.35.654.33 Lost connection

Server.properties is configured correctly, and I'm running in online mode.

What could be the problem?

Solution 1:

Try putting your server in offline mode. Offline\online mode involves your server talking with the Mojang servers to find out if your players have an actual account and whatnot. More often than not 'bad login' is a result of this 'handshaking' process taking too long.

Setting your server to offline mode does have its problems however, it allows people with hacked clients to join your server, and it also allows people with some java knowledge to join your server posing as other players. This can lead to some severe griefing. That said, if your only playing with friends that you know then I don't think these issues will come up. I highly advise you DO NOT put your server in offline mode if it is a public server but other than that, it's worth a try.