in Magento

Call to undefined method Mage_Admin_Model_Observer::actionPostDispatchAdmin()

I upgraded Magento to 1.4.0.0 to 1.4.0.1 and got the following error:

Call to undefined method Mage_Admin_Model_Observer::actionPostDispatchAdmin()

Everything inside /var/sessions/ and /var/cache and (if it exists) /app/code/core/Zend/Cache/ must be deleted.