ftp_put() [function.ftp-put]: Failed to establish connection

I'm trying to ftp upload file using php. Managed to connect via ftp_connect, and ftp_login. That means the connection / credential's ok. However when I try to run ftp_p开发者_如何学Pythonut, it comes out with that error.

ftp_put() [function.ftp-put]: Failed to establish connection

Anyone know what could be causing that problem?