Only in privatemsg_sub: pm_tags
diff -urp privatemsg/privatemsg.module privatemsg_sub/privatemsg.module
--- privatemsg/privatemsg.module	2008-10-14 18:00:41.000000000 +0100
+++ privatemsg_sub/privatemsg.module	2008-10-22 16:56:14.036612200 +0100
@@ -232,11 +232,13 @@ function privatemsg_list($uid = NULL) {
     if ($uid && $uid == $user->uid) { // Viewing our own messages.
       $account = $user;
     }
-    else if ($uid && $uid != $user->uid && user_access('read all private messages')) {
+    elseif ($uid && is_numeric($uid) && $uid != $user->uid && user_access('read all private messages')) {
       $account = user_load(array('uid' => $uid));
     }
     else { // We tried viewing someone else's messages but didn't have sufficient rights.
-      drupal_set_message(t("You do not have sufficient rights to view someone else's messages"), WATCHDOG_WARNING);
+      if (is_numeric($uid)) {
+        drupal_set_message(t("You do not have sufficient rights to view someone else's messages"), WATCHDOG_WARNING);
+      }
       $account = $user;
     }
   }