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

System.NullReferenceException: Object reference not set to an instance of an object.
   at Dynamicweb.Ecommerce.ProductCatalog.ViewEngine.CreateProductGroup(ProductGroupViewModelSettings settings, ViewModelPropertyFiller`1 filler, Group group)
   at Dynamicweb.Ecommerce.ProductCatalog.ViewModelPropertyFiller`1.Fill[S](T model, String propertyName, Func`1 source)
   at Dynamicweb.Ecommerce.ProductCatalog.ViewEngine.CreateView(ProductListViewModelSettings settings, Group group, IList`1 products)
   at Dynamicweb.Ecommerce.ProductCatalog.ProductCatalogFrontend.RenderProductList(ProductCatalogSettings settings, String groupId)
   at Dynamicweb.Ecommerce.ProductCatalog.ProductCatalogFrontend.GetContent()
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)