Invalid form Submission in WordPress wp_handle_upload. Sometime, we face the issue of `Invalid form Submission` . I have a solution for the problem. It actually occurs when you pass single argument to the `wp_handle_upload`.  your code might be like the below one. $file = wp_handle_upload($_FILES['upload_file']); You have to add one more parameter with it. $file = wp_handle_upload($_FILES['upload_file'], array('test_form' => FALSE)); This one solves your problem ...