Magento Product Creation error...SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry?

In Magento's Product creation code, I add my own custom code in /htdocs/magento/app/code/core/Mage/Adminhtml/controllers/Catalog/ProductController.php I have make external mysql connection & use that for inserting product id & sku in custom table.(I know this is not recommended way but just for testing purpose I am doing this.) My code-: public function saveAction() { $storeId