Hi,
are you running IOSFW (CBAC) on this router? The only way to reconfigure ftp client is on your client itlself. Windows FTP client is by default active and I dont think you can change it to use passive mode. You can use other gui ftp clients to use passive mode though. I guess I understood why passive FTP is working and not active FTP. With Passive FTP both the connectiions to the FTP server are initiated by the client (inside) , hence they are allowed through and the return traffic as well. but in active FTP; server port tcp/20 also initiates a connection to client at port > 1024. Now your IOS should be sophisticated enogh e.g. running CBAC to inspect the port transmission on the control channel , hencing opening up the ports for the data channel. Otherwise you need to explicitly permit it e.g.
permit tcp any eq 20 any gt 1024
Thanks
Nadeem