FTP Error - econnrefused - connection refused by server

[genesis_mp]

Hi there,

I am using multiple WAN connections (WAN1 and WAN2). Every thing is working fine but FTP wont work well.
No solutions worked so far.

If i connect to my FTP server, my FTP server responds and connects correct. First it shows the listing of folder and then disconnect me after some time or when i navigate to subfolders. I tried with multiple FTP Software and Filezila show this Error:

Status:      Resolving address of ftp.mydomain.de
Status:      Connecting to 81.xxx.xxx.xxx:21…
Status:      Connection established, waiting for welcome message...
Status:      Server does not support non-ASCII characters.
Status:      Logged in
Status:      Retrieving directory listing...
Command: PWD
Response: 257 "/" is current directory.
Command: TYPE I
Response: 200 Using BINARY mode to transfer data.
Command: PASV
Response: 227 Entering Passive Mode (81,169,145,47,189,96)
Command: MLSD
Error:        The data connection could not be established: ECONNREFUSED - Connection refused by server
Response: 150 Opening ASCII mode data connection.

Firewall Rules are:
Protocol    Source              Port    Destination    Port    Gateway

Ipv4          LAN1 / LAN2      any    any              21      WAN1 (also tried WAN1_and_WAN2)

Does anyone know what i can do to fix this?...  :-\

Thanks
David