ok i guess i should have given more info. im using a linksys WRT320N and a qnap ts 859 nas. I set port 21 to forward to my nas. in the configuration for the nas you can specify which port to use. as i said if i change both setting to port 21 it works no problem.
Please read the link I posted. Figure out whether you are using Passive or Active FTP on the client. If you are using Active you will likely have to forward the Data port/connection on the client side. If you are using Passive you likely will need to forward the Data port/connection on the Linksys(server side). Port 21 is the control port/connection.
As I said most routers have special routines that deal with FTP because it uses 2 ports and therefore when you are not using port 21 they may not know they need to allow the connection on a different port. -- Warning, If you post nonsense and use misinformation and are here to argue based on those methods, you will be put on ignore.