If you are having trouble with your FTP login even though you entered the correct username and password, there is a high possibility that this problem was due to SELinux.
I've encountered this problem on my CentOS 6 box and after disabling SELinux, the issue is resolved! To disable SELinux (for CentOS 6):
- Change value
- Reboot your server
Hope it helps! It took me hours to get this solved.