Unable to list SFTP Directory on windows 2008 r2 server from internet

Hi experts,

I have configured a SFTP on windows 2008 r2 server. And i am using the Filezilla on client machine to connect to SFTP server.

The connection works properly on internal network but it displays error when i connect from internet.

Error: GnuTLS error -53: Error in the push function.
Response: 550 Data channel timed out.
Error: Failed to retrieve directory listing

This machine is publish with public IP and port22. The connection and authorization process gets complete but stops are Directory Listing.

PLease suggest the troublshooting steps..

Let me know if any more info is rquired.