I have a problem with one particular site that throws this error periodically
Fatal error: Cannot override final method Mage_Core_Model_Abstract::clearInstance() in app/code/core/Mage/Catalog/Model/Product.php on line 39
I clear cache : Didn't work I restart apache : Site comes back.
EDIT: I am getting the same error in Admin in the products section as well.
I am not running memecache or REDIS or APC
PHP Version 5.3.29