Why am I getting HTTP: 500 Internal Server Error when I am trying to use after_retrieve?

Question

I am trying to use logic hook 'after_retrieve', but I keep getting a 500 Internal Server Error when it is trying to load records into the subpanel. 
 
 It happens whether I have something called by after_retrieve or even just set it as an empty array. 
 
 I even tried 'after_fetch_query', but that never runs anything. $hook_array{'after_retrieve'] = Array();
$hook_array['after_retrieve'] = Array(11, "Check Whether to Highlight Title","custom/Resources/logic_hooks/Courses_Logic_Hooks.php", "Courses_Logic_Hooks", "setAlertField",);

Amy Cox · Accepted Answer

500 errors are almost always syntax errors, you have an error on line 1, you are opening a curly bracket instead of a square bracket :) 
 
 $hook_array { 'after_retrieve'] = Array(); 
 should be 
 $hook_array['after_retrieve'] = Array(); 
 
 FrancescaS