Random PHP error...

My site was up and running fine for a month or two, but then today it threw this error... (it’s only on the homepage, everything else is accessible).

PHP error debug
Error: require_once(manager/includes/sniff/phpSniff.core.php) [function.require-once]: failed to open stream: No such file or directory
Error type/ Nr.: Warning - 2
File: D:\Inetpub\graygiant\manager\includes\sniff\phpSniff.class.php
Line: 22
Line 22 source: require_once($modx->config[’base_path’] . ’manager/includes/sniff/phpSniff.core.php’);

HELP! What do I do?

Find out who deleted that file? Or simply put it back in it’s place and start looking for another hosting provider? But seriously, sounds like someone removed the file for some reason. Start looking in the location specified in the error and see if the file is there or not.

The file is there! I don’t know what’s going on...

What do I do if the file is still there?