Something that isn't mentioned above is that although ftp_ssl_connect may be available and will return an FTP stream it may not be usable. Take the following code (FTP login credentials are obviously set elsewhere):
$ftp_connection = @ftp_ssl_connect($this->ftp_host);
$ftp_connection = @ftp_connect($this->ftp_host);
ftp_login($ftp_connection, $this->ftp_user, $this->ftp_password);
From this you'd assume everything would work, ftp_ssl_connect is available and you have a connection. However, once you get to ftp_login, you could get this:
Warning  ftp_login() [function.ftp-login]: AUTH not understood
This is because the server is not configured to understand the encrypted details, even though the function is available and an SSL-FTP stream was opened.
If you are trying to use ftp_ssl_connect make sure you check if you can login after using it, and if not, connect again with standard ftp_connect.
Hope this is of use.