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

System.NullReferenceException: Object reference not set to an instance of an object.
   at Highsun.OnAfterGenerateProductInfoXmlSubscriber.OnNotify(String notification, NotificationArgs args)
   at Dynamicweb.Extensibility.Notifications.NotificationManager.Notify(String notification, NotificationArgs eventArgs)
   at Dynamicweb.Ecommerce.LiveIntegration.XmlGenerators.ProductInfoXmlGenerator.GenerateProductInfoXml(Dictionary`2 products, ProductInfoXmlGeneratorSettings settings)
   at Dynamicweb.Ecommerce.LiveIntegration.Products.ProductManager.BuildProductRequest(Dictionary`2 products)
   at Dynamicweb.Ecommerce.LiveIntegration.Products.ProductManager.FetchProductInfos(Dictionary`2 products, User user, Boolean updateCache)
   at Dynamicweb.Ecommerce.LiveIntegration.NotificationSubscribers.NotificationSubscriberBase.SetProductsInfo(Dictionary`2 products, User user)
   at Dynamicweb.Ecommerce.LiveIntegration.NotificationSubscribers.NotificationSubscriberBase.SetProductInformation(Product product, Double quantity)
   at Dynamicweb.Ecommerce.LiveIntegration.NotificationSubscribers.ProductBeforeRender.OnNotify(String notification, NotificationArgs args)
   at Dynamicweb.Extensibility.Notifications.NotificationManager.Notify(String notification, NotificationArgs eventArgs)
   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)