ip_conntrack_ftp and ip_nat_ftp are used for active ftp to allow the data channel on port 20 to be handled correctly..
It's time to start looking more closely at the individual packets, prob with tcpdump.
Have a look at man tcpdump
and the examples later in the page.
Make sure replies are returning correctly.
The programme wget
exists for M$ so you can use some of it's passive/active options to test with.