Why can't I add a product to my cart?

The error message: "Info: To add this product into your cart you have to select a product variant on the details page." appears, and you cannot add the product to your shopping cart. Please wait after you have selected the size or color of the item for the shipping method drop down menu to appear. Then, click "Add to Cart." The error message should disappear. If you are still having problems, please call us toll-free at 1-866-K9-CARTS (1-866-592-2787).