The unique SKU of the products is not being set when the products are created. To add unique SKU with products, then follow the instructions given below.
1) Add a custom text field with _sku to the product form.
2) Add the following code inside the theme’s functions.php file.
GeSHi Error: GeSHi could not find the language php (using path /home/mahbktbn/public_html/wp-content/plugins/codecolorer/lib/geshi/) (code 2)
3) Now, try to submit a product using the frontend product form. Use an existing SKU related to other product. You will see the following error.