I did an upgrade from 1.5 to 1.9 but after the upgrade I get the following error:
Fatal error: Call to undefined method Mage_Core_Model_App::getIsCacheLocked() in /var/www/demanchetknopenwinkel/app/code/core/Mage/Core/Model/Resource.php on line 112
I followed the steps from the site duntuk.com to upgrade but after that, no go.
Reindexing also gives the same problem.
Any idea on how to fix?