Hi,
you might try checking out my previous post and the other guys tip to disable SSL, if you enabled it. http://forums.dlink.com/index.php?topic=42217.0 , it might help. Also, there are some Dlink tutorials on youtube which might help you setup your ftp server and a few other options. They are below, but I forget which is the ftp one. A little trial and error should help get you set up. Good luck.
http://www.youtube.com/watch?v=rL8F6k-X8xs
http://www.youtube.com/watch?v=BCxdGWmrcOM&feature=related
http://www.youtube.com/watch?v=0jAjEr_UQHM