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.GroupRelation.get_GroupRelationsByChildId(String childId)at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldGroupValueService.GetOrderedInheritableParentIds(GroupInformation group)at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldGroupValueService.RecursivelySearchForFieldValues(GroupInformation group, String defaultLanguageId, List`1 categoryFields)at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldGroupValueService.SearchForGroupFieldValue(GroupInformation group, String defaultLanguageId, List`1 categoryFields, Boolean allowFallback)at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldGroupValueService.GetGroupCategoryFieldValues(GroupInformation group, String defaultLanguageId, List`1 fields, Boolean allowFallback)at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldGroupValueService.GetDefaultCategoryValuesFromGroups(IEnumerable`1 groupInfos, String defaultLanguageId, List`1 catFields)at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldGroupValueService.GetDefaultCategoryValueFromGroups(IEnumerable`1 groupInfos, String defaultLanguageId, Field catField)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.Products.Categories.ProductCategoryFieldValueService.GetProductCategoryFieldValue(Product product, String categoryId, Field field)at Dynamicweb.Ecommerce.Frontend.Renderer.RenderProductCategories(Product product, Template template, String loopName, Lazy`1 categoryFieldSortings)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.RenderProduct(Product product, String unitId)at Dynamicweb.Ecommerce.Frontend.Frontend.EcomRender()at Dynamicweb.Ecommerce.Frontend.Frontend.GetContent()at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)