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

System.ArgumentException: An item with the same key has already been added.
at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
at Dynamicweb.Ecommerce.Products.GroupRelation.GetGroupRelationsByChildId(String childId)
at Dynamicweb.Ecommerce.Products.Group.GetParentGroupsByLanguageId(String languageId)
at Dynamicweb.Ecommerce.Products.Categories.CategoryExtensions.GetGroupIds(IEnumerable`1 groupCollection, Dictionary`2 groupsToValueLoadById)
at Dynamicweb.Ecommerce.Products.Categories.CategoryExtensions.GetGroupIds(IEnumerable`1 groupCollection, Dictionary`2 groupsToValueLoadById)
at Dynamicweb.Ecommerce.Products.Categories.CategoryExtensions.LoadCategoryValues(IEnumerable`1 groups)
at Dynamicweb.Ecommerce.Products.ProductCollection.LoadProductCategoryValues()
at Dynamicweb.Ecommerce.Frontend.Frontend.ListProducts(ProductCollection products, String groupsIdent, Boolean hasBeenSorted)
at Dynamicweb.Ecommerce.Frontend.Frontend.GetProductsFromIndexQuery(ProductCatalogShowType settingsType)
at Dynamicweb.Ecommerce.Frontend.Frontend.EcomRender()
at Dynamicweb.Ecommerce.Frontend.Frontend.GetContent()
at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)