Fatal error: Cannot override final method Mage_Core_Model_Abstract::clearInstance() in /app/code/core/Mage/Core/Model/Store.php on line 35
I’ve been getting this error in the server log at odd times on a Magento site that I moved to a new server recently. With almost no identical errors showing up in a Google Search, it was being quite a headache to diagnose. Basically at the checkout, users were being redirected back to the cart as soon as the shipping calculation occurred. Occasionally when editing a product, a Bad Gateway error also occurred. My assumption was it must be caused by an extension trying to override the core, however, the server had a lot of differences to the old one, Nginx instead of Apache, PHP 5.4.12 instead of 5.3, ISPConfig instead of cPanel, and the list goes on. I had no idea where to start.
I had an issue earlier where Zend in the PHP 5.4 was incompatible with a couple of lines of code in Magento, I had already fixed this, but I decided to try rolling PHP back to 5.4.11 and rebuild it just to see what would happen.
It solved it, I’m still not sure entirely what the cause was, but hopefully this helps someone else if they encounter the same issue.