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.GetGroupAssets(MediaViewModelSettings settings, Group group)
   at Dynamicweb.Ecommerce.ProductCatalog.ViewEngine.CreateProductGroup(ProductGroupViewModelSettings settings, ViewModelPropertyFiller`1 filler, Group group)
   at Dynamicweb.Ecommerce.ProductCatalog.ViewEngine.FillGroup(ProductListViewModelSettings settings, Group group, ProductListViewModel model, ViewModelPropertyFiller`1 filler)
   at Dynamicweb.Ecommerce.ProductCatalog.ViewEngine.CreateView(ProductListViewModelSettings settings, Group group, IList`1 products)
   at Dynamicweb.Ecommerce.ProductCatalog.ViewModelFactory.CreateView(ProductListViewModelSettings settings, String groupId, IEnumerable`1 productAutoIds)
   at Dynamicweb.Ecommerce.ProductCatalog.ProductCatalogFrontend.RenderProductList(ProductCatalogSettings settings, QuerySettings querySettings, IQuery query, String groupId, Boolean feed, Boolean compare)
   at Dynamicweb.Ecommerce.ProductCatalog.ProductCatalogFrontend.GetModuleContent()
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)