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

System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
   at Dynamicweb.Ecommerce.LiveIntegration.Products.ProductManager.SaveLastResponse(Boolean fetchResponse)
   at Dynamicweb.Ecommerce.LiveIntegration.Products.ProductManager.FetchProductInfos(Dictionary`2 products, User user, Boolean updateCache)
   at Dynamicweb.Ecommerce.LiveIntegration.Products.ProductManager.FetchProductInfos(List`1 products)
   at Dynamicweb.Ecommerce.LiveIntegration.Products.ProductPriceProvider.PreparePrices(ProductCollection products)
   at Dynamicweb.Ecommerce.Prices.PriceManager.PreparePrices(IEnumerable`1 products)
   at Dynamicweb.Ecommerce.Products.ProductRelatedGroupService.GetProductRelations(Product product, String languageId, Boolean isFrontend)
   at Dynamicweb.Ecommerce.Frontend.Renderer.RenderProductRelatedGroups(RenderingContext renderingContext, Product product, Template parentTemplate, String loopName)
   at Dynamicweb.Ecommerce.Frontend.Renderer.RenderProduct(Product product, Boolean extendedProperties, Template template, Int32 loopCounter, Boolean renderRelated, String productUrl, Int32 quantity, Int32 wishListId, Boolean renderPublicList, Boolean isRecursiveCall, Lazy`1 categoryFieldSorting, Int32 orderLineOfProductCount, RenderingContext renderingContext, String unitId)
   at Dynamicweb.Ecommerce.Frontend.Renderer.RenderProduct(Product product, Boolean extendedProperties, String unitId)
   at Dynamicweb.Ecommerce.Frontend.Frontend.RenderProduct(Product product, String unitId)
   at Dynamicweb.Ecommerce.Frontend.Frontend.EcomRender()
   at Dynamicweb.Ecommerce.Frontend.Frontend.GetContent()
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)