King make sure the edit is directly below <?php i.e.
PHP Code:
<?php
define('DISABLE_HOOKS', true);
/*======================================================================*\
When done comment it out by adding // in front i.e.
PHP Code:
<?php
// define('DISABLE_HOOKS', true);
/*======================================================================*\
Then you don't have to hunt it down later on

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Also what are you using to edit? sometimes using wordpad or notepad on a windows pc then pasting code into interfaces on a linux/unix can add in extra characters when posting and you may not even see them initially so be sure to use something free like notepad++ or similar when editing files

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