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

System.NullReferenceException: Object reference not set to an instance of an object.
   at Dynamicweb.eCommerce.Products.Categories.Category.GetCategoryByID(String categoryID, String languageID)
   at Dynamicweb.eCommerce.Products.Categories.Field.CachedFields()
   at Dynamicweb.eCommerce.Products.Categories.Field.GetFieldsByCategoryId(String categoryId, String languageId)
   at Dynamicweb.eCommerce.Products.Categories.Category.get_Fields()
   at Dynamicweb.eCommerce.Frontend.Renderer.RenderProductCategoryFields(Product product, Category category, Template template, String loopName)
   at Dynamicweb.eCommerce.Frontend.Renderer.RenderProductCategories(Product product, Template template, 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, Int32 orderLineOfProductCount)
   at Dynamicweb.eCommerce.Frontend.Renderer.RenderProduct(Product Product, Boolean ExtendedProperties)
   at Dynamicweb.eCommerce.Frontend.Frontend.EcomRender()
   at Dynamicweb.eCommerce.Frontend.Frontend.GetContent()
   at Dynamicweb.Frontend.Content.GetModule(DataRow& ParagraphRow)