Index: ucp_pm_viewfolder.php
===================================================================
--- ucp_pm_viewfolder.php	(revision 10122)
+++ ucp_pm_viewfolder.php	(working copy)
@@ -314,12 +314,18 @@
 
 						$result = $db->sql_query($sql);
 
+						$new_address = array();
 						while ($info_row = $db->sql_fetchrow($result))
 						{
-							$address[$message_id][$ug_type][$address[$message_id][$ug_type][$info_row['id']]][] = $info_row['name'];
+							$new_address[$ug_type][$address[$message_id][$ug_type][$info_row['id']]][] = $info_row['name'];
 							unset($address[$message_id][$ug_type][$info_row['id']]);
 						}
 						$db->sql_freeresult($result);
+						foreach ($address[$message_id][$ug_type] as $user_id => $type)
+						{
+							$new_address[$ug_type][$address[$message_id][$ug_type][$type]][] = 'Unknown ('.$user_id.')';
+						}
+						$address[$message_id] = $new_address;
 					}
 				}