So then, now you know the problem's not with your router.
I would say it's a 90% chance that it's a patch problem.
1) Uninstall KO.
2) Download THIS client.
3) Go to ftp://download.knightonlineworld.com/knight/upgrade/
4) Download Patches 1506 - 1509, installing each one after you download it.
It seems basic, I know, but it's easy to screw up.
Hopefully that helps.