--- tac_lite.module.orig	2009-04-17 16:46:34.000000000 +0200
+++ tac_lite.module	2009-04-17 16:46:53.000000000 +0200
@@ -426,7 +426,7 @@ function _tac_lite_user_tids(&$account, 
   // add per-role grants in addition to per-user grants
   $defaults = variable_get('tac_lite_grants_scheme_' . $scheme, array());
   foreach ($account->roles as $rid => $role_name) {
-    if (count($defaults[$rid])) {
+    if (isset($defaults[$rid]) && count($defaults[$rid])) {
       foreach ($defaults[$rid] as $tids) {
         if (count($tids)) {
           $grants = array_merge($grants, $tids);