Forgot to add the code for the actual div that's shown:

Code:
<div id="message"><?php
  // Display all header alerts via messageStack:
  if ($messageStack->size('header') > 0) {
    echo $messageStack->output('header');
  }
  if (isset($_GET['error_message']) && zen_not_null($_GET['error_message'])) {
  echo htmlspecialchars(urldecode($_GET['error_message']));
  }
  if (isset($_GET['info_message']) && zen_not_null($_GET['info_message'])) {
   echo htmlspecialchars($_GET['info_message']);
} else {

}
?></div>