help with SUSEFirewall2 and FTP

I am still working on setting up an FTP-server in DMZ. I did what Robert Klein suggested, and it helped. External access is working, but the access from internal is only working halfway. I can connect from internal to ftp and i can login ok, but when the dataconnection is being established the firewall is dropping the conn. from FTP-server to internal. I know that it is the conn. to port 20 thats is the problem. Is there anyone who can tell me what's wrong and come up with a solution Thanks in advance Lars Christiansen