Index: privatemsg.module
===================================================================
RCS file: /cvs/drupal/contributions/modules/privatemsg/privatemsg.module,v
retrieving revision 1.70.2.30.2.91.2.25
diff -u -p -r1.70.2.30.2.91.2.25 privatemsg.module
--- privatemsg.module	22 Feb 2009 21:21:08 -0000	1.70.2.30.2.91.2.25
+++ privatemsg.module	11 Mar 2009 07:48:17 -0000
@@ -1232,6 +1232,11 @@ function _privatemsg_validate_message(&$
 
   if (!empty($message['recipients']) && is_array($message['recipients'])) {
     foreach ($message['recipients'] as $uid => $recipient) {
+      if (!is_object($recipient) || !isset($recipient->uid)) {
+        $errors[] = t('Incorrect recipient format, recipients needs to be an array of user objects. Actual value: %recipient', array('%recipient' => $recipient));
+        unset($message['recipients'][$uid]);
+        continue;
+      }
       $block_results = module_invoke_all('privatemsg_block_message', $author, $recipient);
       if (count($block_results) > 0) {
         unset($message['recipients'][$uid]);