Index: includes/bootstrap.inc
===================================================================
--- includes/bootstrap.inc      (revision 1817)
+++ includes/bootstrap.inc      (working copy)
@@ -654,6 +654,10 @@
  *   - 'error'
  */
 function drupal_set_message($message = NULL, $type = 'status') {
+  if ($type == 'error') {
+    $message .= print_r(debug_backtrace(), 1);
+  }
+
   if ($message) {
     if (!isset($_SESSION['messages'])) {
       $_SESSION['messages'] = array();