For anyone that may have this issue.
We were able to solve the problem. Apparently, the plugin doesn’t swith to passive, even though it’s checked.
We had to edit the file CdnEngine_Ftp.php and add the following line right before the code starts any uploads (specifically, on lines #228 and #363:
@ftp_pasv( $this->_ftp, true );
As you can see from above, we’re hard coding the code to use always use passive, that would have to be modified to use passive based on the user selection on the GUI.
Hope it helps someone!