This plugin creates a log entry every time the error_no_permission function is called by MyBB.  It logs the user id, the timestamp, the value of THIS_SCRIPT if it is defined or $_SERVER['PHP_SELF'] if it is not, and the full url the user attempted to reach.  Entries are viewed in the Admin CP under Tools & Maintenance.  You are able to sort entries by username, time (default), and Script.  50 entries are available per page with pagination enabled.  There is an admin permission for viewing the log in case you don't want all Administrators to have access to it since full urls are revealed.