Trouble with problem "500"

Iam having some trouble using smart ftp and hope you guys could help me. When i start transferin files to my webserver (from my pc to the webserver) after a while smart ftp comes with this message: 500 - I won't open a connection to 192.164.1.x (only to and stop the transfer. Iam uploading it behind a router, so this could be a problem "server-side" or "client-side"? Is there something i can configure in smart ftp?
thanks for any help.

Forgot to tell that i found a solution (PORT to PASV mode) but my server does not allow PASV mode so i can't connect.

Hi, you can force PORT to show your public ip address (play with port ip modes).

i undesrstood what you said, but how can i do it? i already oppened a port in my router, so i configure "PORT Mode" to manual and my port there? thanks for the help.