Magento Invalid Method Mage Catalog Model Product IsDuplicable

New version theme is not working in old version.

After upgrading magento or when I design theme in magento 1.5.0.1 and use that theme in magento 1.4.2 that time my product page shows error like

Invalid method Mage_Catalog_Model_Product::isDuplicable

I find the solutin and its work for me.

Copy your product.php file from this path: app\code\core\Mage\Catalog\Model\product.php and replace in your maegnto folder.