Index: lib/action/opMessagePluginMessageActions.class.php
===================================================================
--- lib/action/opMessagePluginMessageActions.class.php	(リビジョン 13346)
+++ lib/action/opMessagePluginMessageActions.class.php	(作業コピー)
@@ -249,7 +249,7 @@
   public function executeReply(sfWebRequest $request)
   {
     $message = SendMessageDataPeer::retrieveByPk($request->getParameter('id'));
-    $this->forward404unless($message);
+    $this->forward404unless($message && $message->getIsReceiver($this->getUser()->getMemberId()));
     $this->message = new SendMessageData();
     $this->message->setMessageTypeId($message->getMessageTypeId());
     $this->message->setReturnMessageId($message->getId());