Originally Posted by RdeN
I get ECONNREFUSED - Connection refused by server messages if I try to reach my FTP server from the outside.
I use port 20,21. I know this will conflict with the FTP access to the RT-N66U itself.
As Merlin said; make sure the built-in ftp module is disabled. If disabled there should be no conflicts with ports 20-21 for the non buit-in ftp server.
Apparently you did not change the configuration the last time with the older firmware, so for now go to the menu of the router gui. Go to USB application > Servers center > FTP share > Disable ftp