Description
In one of the latest version rebuilds appeared a bug when you can't add products from Special Offers block.
 
Solution
Download the updated version of the file:
http://www.viart.com/downloads/shopping_cart-4.0.7.zip
 
Further, extract 'shopping_cart.php' into 'includes' folder of your shop via FTP in BINARY mode replacing an existing file. Please do not forget to make a backup copy of the current file in case something goes wrong.