Log the user before it gets deleted to see why it dies

auth.php

@@ -389,6 +389,7 @@ class auth_plugin_ldap_syncplus extends auth_plugin_ldap {
                     $graceperiod = max(intval($this->config->removeuser_graceperiod), 0);
                             // Fix problems if grace period setting was negative or no number.
                     if (time() - $user->timemodified >= $graceperiod * 24 * 3600) {
+                        mtrace(sprintf("\t try to delete user: %s (%d)", $user->username, $user->id));
                         if (delete_user($user)) {
                             mtrace("\t".get_string('auth_dbdeleteuser', 'auth_db', array('name'=>$user->username, 'id'=>$user->id)));
                         } else {