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

System.NullReferenceException: Object reference not set to an instance of an object.
at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldGroupValueService.GetOrderedInheritableParentIds(Group group, String defaultLanguageId)
at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldGroupValueService.RecursivelySearchForFieldValues(Group group, String defaultLanguageId, List`1 categoryFields)
at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldGroupValueService.RecursivelySearchForFieldValues(Group group, String defaultLanguageId, List`1 categoryFields)
at System.Lazy`1.ViaFactory(LazyThreadSafetyMode mode)
at System.Lazy`1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor)
at System.Lazy`1.CreateValue()
at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldGroupValueService.GetGroupFieldValuesByLanguage(Group group, List`1 categoryFields, String languageId, Boolean isInheritedValue, Boolean searchRecursively)
at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldGroupValueService.GetGroupCategoryFieldValues(IEnumerable`1 groups, List`1 fields, Boolean allowFallback)
at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldGroupValueService.GetDefaultCategoryValuesFromGroups(IEnumerable`1 groupInfos, List`1 catFields)
at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldValueService.GetProductCategoryFieldValue(Product product, String categoryId, Field field)
at Dynamicweb.Ecommerce.ProductCatalog.ViewEngine.CreateView(ProductViewModelSettings settings, Product product, Field field)
at Dynamicweb.Ecommerce.ProductCatalog.ViewEngine.GetFieldDisplayGroupValues(ProductViewModelSettings settings, Product product, String languageID, Lazy`1 productIds)
at Dynamicweb.Ecommerce.ProductCatalog.ViewEngine.<>c__DisplayClass3_1.b__59()
at Dynamicweb.Ecommerce.ProductCatalog.ViewModelPropertyFiller`1.Fill[S](T model, String propertyName, Func`1 source)
at Dynamicweb.Ecommerce.ProductCatalog.ViewEngine.BulkCreateView(ProductViewModelSettings settings, Boolean isRecursive, IList`1 products)
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)
at Dynamicweb.Ecommerce.ProductCatalog.ProductCatalogFrontend.GetModuleContent()
at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)