Strange problem in a plug-in

[sv1cec]

I am trying to use a simple query in a plug-in, located in the postbit_display_start hook, and for some strange reason, it crashes with the following error:

Fatal error: Call to a member function on a non-object in /home/xxx/xxx/includes/class_postbit.php(251) : eval()'d code on line 80

The code in that line, looks like:

$get_notes=$db->query_read("select w.*, u.username as warner from ".TABLE_PREFIX."warn_notes w
			LEFT JOIN ".TABLE_PREFIX."user u on (u.userid=w.warned_by)
			where warned_user='{$post[userid]}' order by warned_time desc");

I am not familiar with the new 3.5 conventions, but I can't find anything wrong with that statement, so any help would be greatly appreciated.

Rgds