Maximum key size must be smaller 32 Magento

1.-Flush your cache if it doesnt work check PHP version it must be 5.5.
     Write in any file <?php echo 'Versión actual/Actual version  PHP: ' . phpversion(); ?>

2.-If it doesnt work check the app/etc/local.xml file an change your line instead this one

  <key><![CDATA[ec9d0046fcf435bc516ea43bab9798fa]]></key>