Alright, time for another quick tip, If you've already gone through the Drupal quick fix for the ereg to mb_ereg change on line 911 of your file.inc problem you may be like me - unable to open anything after a restart.

Here is the fix: Try to restart apache directly like this

sudo /etc/init.d/apache2 restart

If the error arises it will highlight which file is missing in this folder:

/etc/apache2/conf.d/THISFILE

In my case it was a remnant from Ampache the music daemon. I deleted it and restarted apache again.

sudo rm /etc/apache2/conf.d/THISFILE