Fatal Error leads to WSOD

I am not sure what caused this error to start. I am getting a WSOD when trying to access

admin/structure/types/manage/CONTENT_TYPE/fields

Adding error reporting to index.php produces following error message:

Fatal error: Cannot increment/decrement overloaded objects nor string offsets in /var/www/html/sites/all/modules/field_tools/field_tools.module on line 288

Ref: How to add error reporting to Index.php. https://drupal.org/node/158043

Note the requirement to add these lines to the top of the file:

<?php
error_reporting(E_ALL);
ini_set('display_errors', TRUE);
ini_set('display_startup_errors', TRUE);
// $Id: index.php,v 1.94 2007/12/26...

Also, DO NOT include the <?php line