AddToCart function with Product Attribute NopCommerce 1.90

It seems AddToCart function is not adding same product to the cart with different Attributes selection.
First time a product with size:8, color:black added to cart.
Second time same production with size:9, color:white can't add to the cart. There is no error message as well.

Below function also does not return any CartWarnings. I checked in debug mode and the attributes are different for the same product.
List<string> addToCartWarnings = this.ShoppingCartService.AddToCart(
                            ShoppingCartTypeEnum.ShoppingCart,
                            pv.ProductVariantId,
                            attributes,
                            customerEnteredPriceConverted,
                            quantity);

FOUND SOLUTION: GlobalSettings.Products had "Maximum ShoppingCart Item" = 1. I changed it to desired number and works fine.