An error occured while attaching module (Dynamicweb.Frontend.Content)

    System.NullReferenceException: Object reference not set to an instance of an object.
       at Dynamicweb.eCommerce.Orders.Discounts.Discount.GetOrderLineDiscounts()
       at Dynamicweb.eCommerce.Orders.Discounts.DiscountInfoCollection.LoadDiscounts()
       at Dynamicweb.eCommerce.Products.Product.DiscountMatrix()
       at Dynamicweb.eCommerce.Frontend.Renderer.RenderProduct(Product Product, Boolean ExtendedProperties, Template Template, Int32 loopCounter, Boolean renderRelated, String productURL, Int32 quantity, Int32 wishListID, Boolean renderPublicList, Int32 orderLineOfProductCount)
       at Dynamicweb.eCommerce.Frontend.Renderer.RenderProducts(ProductCollection Products, Template ParentTemplate, String LoopName, Int32 LoopCounter, Boolean renderRelatedProducts, Boolean renderRelatedLists)
       at Dynamicweb.eCommerce.Frontend.Renderer.RenderRelatedProductLists(Template template, RelatedProductListProviderEventArgs relatedParams)
       at Dynamicweb.eCommerce.Frontend.Renderer.RenderProduct(Product Product, Boolean ExtendedProperties, Template Template, Int32 loopCounter, Boolean renderRelated, String productURL, Int32 quantity, Int32 wishListID, Boolean renderPublicList, Int32 orderLineOfProductCount)
       at Dynamicweb.eCommerce.Frontend.Renderer.RenderProduct(Product Product, Boolean ExtendedProperties)
       at Dynamicweb.eCommerce.Frontend.Frontend.RenderProduct(Product prod)
       at Dynamicweb.eCommerce.Frontend.Frontend.EcomRender()
       at Dynamicweb.eCommerce.Frontend.Frontend.GetContent()
       at Dynamicweb.Frontend.Content.GetModule(DataRow& ParagraphRow)