Index: privatemsg.module
===================================================================
RCS file: /cvs/drupal/contributions/modules/privatemsg/privatemsg.module,v
retrieving revision 1.70.2.30.2.91.2.41
diff -u -p -r1.70.2.30.2.91.2.41 privatemsg.module
--- privatemsg.module	22 Apr 2009 02:23:45 -0000	1.70.2.30.2.91.2.41
+++ privatemsg.module	22 Apr 2009 09:38:10 -0000
@@ -1272,6 +1272,13 @@ 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;
+      }
+    }
     foreach(module_invoke_all('privatemsg_block_message', $message['author'], $message['recipients']) as $blocked) {
       unset($message['recipients'][$blocked['uid']]);
       $messages['warning'] += $block_results;