connection was aborted by the software in your host machine

I get this message when I try to get to a site. I have been there before - I don't know what I did.

Log:
SmartFTP v1.5.990.2
Resolving host name "jukesftpserver.com"
Connecting to xx.xxx.xxx.xx Port: 21
Connected to jukesftpserver.com.
220-JukesFTPServer
WarFTPd 1.82.00-RC10 (Jan 25 2005) Ready

Could it be my router? I don't understand because I can get into other sites (ex - Smartftp site)
The server I am going to says that it must be on my end.
Thanks for reading - any help appreciated.
Thanks again.

most sites use passive mode as it does not depend much on the users configuration - namely the router config. that site, however, has disabled passive mode and you need to use active mode. you should try to enable upnp (universal plug and play) on your router first. if that doesn't work, you have to manually forward router ports, which is a bit more work, but is documented very well (just google for: "your router name" port forwarding).