<?php echo $this->getMessagesBlock()->toHtml() ?>

<?php
$debugObject = Mage::getSingleton('checkout/session')->getMessages();

echo "Last added message: '" . $debugObject->getLastAddedMessage() . "' <br><br>";
echo "getErrors: " . var_dump($debugObject->getErrors()) . " <br><br>";

Last added message: ''

array(0) { } getErrors:

array(1) { [0]=> object(Mage_Core_Model_Message_Error)#137 (6) { ["_type":protected]=> string(5) "error" ["_code":protected]=> string(39) "Ungültiger Benutzername oder Passwort." ["_class":protected]=> string(0) "" ["_method":protected]=> string(0) "" ["_identifier":protected]=> NULL ["_isSticky":protected]=> bool(false) } } getErrors: