fw-1 on nokiaip51

Hi, how can I enable ftp protocol for my lan’s clients to use it with an external ftp server?With my actual configuration I can reach the server and I pass the autentication, but all pc in my lan hang when opening data connection for example sendingthe “ls” command through the command prompt.The rules of the checkpoint policy editor are like this:
source : an internal ip address (hiding nat)
destination: any
service: ftp
action: accept
track: blank
install on: nokiaip51
time: any
I’ve already enabled both “ftp port” and “ftp pasv” data connection in the user interface.All other services works fine, and so, in my opinion it’s not a nat problem.
Can anyone help me?
Thank you in advance