this is how to send a 404 error to robots when you dont want the robots to crawl you page no more so you are not getting any more errors:
for example, you can use this PHP CODE:
<?php
header("HTTP/1.0 404 Not Found");
?>


it works, if you dont believe me, try it,

you can try it if you have a webmaster tools account with google. then you can Fetch as Google