By looking at the URL's what I conclude is that both the php files are on the same page so change your action url from
<form action='/mobile/process.php?o=9&ft=0' method='POST'>
To
<form action='process.php?o=9&ft=0' method='POST'>
A forward slash before the mobile
means it selects the folder from the root.. So you probably don't need that here.
Last but not the least, be sure the file names are proper, and also make sure the cases are same, because the file names are case sensitive.
Note: You may also get 404 error if you are using header('Location:
xyz.php');
on the form processing page, for redirecting the user to
some page after the form processes and you may encounter 404
because
the page on which the script has redirected doesn't exist. so make sure
that the URL is correct if you are using header()