530 Authentication failed after installing router

I have recently switched ISPs from ADSL to cable. And in the process, I've set up a wireless LAN, so I am now behind a router. After making this switch, I am unable to log on to my FTP server, with the error "530 Authentication failed, sorry". If I connect back to my ADSL service, I can log in with no problem. Anyone has any ideas how to solve this problem? Perhaps something to do with port forwarding or whatsoever? Help is greatly appreciated, thanks! =)