unable to use vars in foreach

I'm using PHP 5.0.2 Here is a snippet of my code $post=$_POST;//this is actually happening in an include somewhere else and autoprepended. Works just fine. $modules = simplexml_load_file(MODULES); foreach ($modules->module as $mod) { echo $mod->postName.'<br>'; if (isset($post[$mod->postName])) { die('in post'); .... ..... echo-ing the postName works just fine, but when I get to the checking whether or not the val is set, I get the error: Warning: Illegal offset type in unset in /var/www/..... If I replace $post[$mod->postName] with a hardcoded val, it works $post['news'] The values of $mod->postName are names of checkboxes.