I have a WL-700gE Router and had trouble getting the ftp to work. I read the forums and it seemed many people had the same problem. I finally figured out what I was doing wrong and if you was like me then this should help you.
1st. succesfully update firmware to 1078
2nd. make sure your dyndns account is setup properly and it receives succesful ping replies.
3rd. create a share folder and switched to user based login. make sure the shared folder has everything enabled (nfs cifs ftp www).
4th. create a user account and gave him/her full access to the newly created share
5th This is where I was making my mistake.
At the Virtual Server Window when you open ports make sure that where it says Local IP you put your external(public) IP not your internal. so where it says port range it should be 20:21 and where it says Local IP it should say for example 68.118.54.214 and where it says local port it should say 21.
This worked for me I didnt need to disable Internet firewall either.
I hope this helps Good Luck.