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

System.NullReferenceException: Object reference not set to an instance of an object.
   at Dynamicweb.Ecommerce.ProductCategoryFieldService.ShowField(Field field, Product product)
   at Bluedesk.FieldTypeProviders.FormaatConcat.GetProductValue(Product product, Object fieldValue, String languageId, Dictionary`2 settings)
   at Dynamicweb.Ecommerce.Products.ProductFieldTypeProvider.GetProductValue(Product product, FieldType fieldType, Object fieldValue)
   at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldValueService.GetCategoryValue(Product product, String defaultLanguageId, IEnumerable`1 orderedGroups, Field catField, Boolean includeInheritance)
   at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldValueService.GetCategoryValue(Product product, String categoryId, String fieldId, Boolean includeInheritance)
   at Dynamicweb.Ecommerce.ProductCategoryFieldService.ShowField(Field field, Product product)
   at Dynamicweb.Ecommerce.Frontend.Renderer.RenderProductCategoryFields(Product product, Category category, Template template, String loopName, Lazy`1 categoryFieldSortings)
   at Dynamicweb.Ecommerce.Frontend.Renderer.RenderProductCategories(Product product, Template template, String loopName, Lazy`1 categoryFieldSortings, RenderingContext renderingContext)
   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.RenderProducts(ProductCollection products, Template parentTemplate, String loopName, Int32 loopCounter, Boolean renderRelatedProducts, Boolean renderRelatedLists, Boolean isRecursive, RenderingContext renderingContext)
   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.EcomRender()
   at Dynamicweb.Ecommerce.Frontend.Frontend.GetContent()
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)