I tried to ftp a 7mb file today off my webserver.
I copied this example directly and it told me.
Port command successful
"there was a problem"
I thought it was because of the size.
But I guessed it might be cause of my firewall.
So I made the ftp connection passive:
<?PHP
...
$login_result = ftp_login($conn_id, $ftp_user_name, $ftp_user_pass);
ftp_pasv($conn_id, true);
?>
Ran the script again & it worked fine.
Hope this helps someone