[Zope] FTP Hang after PWD (desperate)

Problem: FTP client hangs after issueing PWD command. We are behind a firewall and the Zope server is behind a firewall I have access to ours but the people who are hosting the server are not very cooperative :-( Searching the message list I find this is due to a NAT problem For testing purposes I allowed every incoming port from the external server to go trough every port here wich I'm not very happy with. Still the ftp connection hangs. Does the Zope FTP server uses other ports then the initialy set 8021 port to communicate? The ftp client is set to passive mode. Running Zope 2.5.1 on RedHat 7.0 with Apache 1.312 Every tip would be very much appreciated TIA Roel