I'm not familiar with this area, and so can't offer any more help than what I gave before. All I can suggest is opening a support ticket and working with them to try to figure out the magic incantation to get it working. You should first (if you haven't already) google ftp_nlist and see what things others have done to fix this problem (it seems to be reasonably common).
BTW, others have said they activated passive mode (via ftp_pasv), so I don't know if you're going in the wrong direction by going to non-passive mode. At least, you're sure you tried passive mode?