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.get_GroupRelationsByChildId(String childId)
   at Dynamicweb.Ecommerce.ProductCategoryFieldService.GetCategoriesFromGroups(List`1& categories, String languageId, HashSet`1& idsHash, IEnumerable`1 groups, Int32 currentLevel, Int32 minLevel, Nullable`1 maxLevel)
   at Dynamicweb.Ecommerce.ProductCategoryFieldService.GetCategoriesFromGroups(List`1& categories, String languageId, HashSet`1& idsHash, IEnumerable`1 groups, Int32 currentLevel, Int32 minLevel, Nullable`1 maxLevel)
   at Dynamicweb.Ecommerce.ProductCategoryFieldService.GetCategoriesFromGroups(List`1& categories, String languageId, HashSet`1& idsHash, IEnumerable`1 groups, Int32 currentLevel, Int32 minLevel, Nullable`1 maxLevel)
   at Dynamicweb.Ecommerce.ProductCategoryFieldService.GetCategoryGroups(IEnumerable`1 groupInfos, String languageId, Int32 minLevel, Nullable`1 maxLevel)
   at Dynamicweb.Ecommerce.ProductCategoryFieldService.GetCategoryGroups(IEnumerable`1 groups, String languageId, Int32 minLevel, Nullable`1 maxLevel, Boolean includeProductProperties)
   at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryService.VB$StateMachine_27_GetCategories.MoveNext()
   at Dynamicweb.Ecommerce.Products.Categories.ProductCategoryFieldValueService.FillProductsValues(IEnumerable`1 products)
   at Dynamicweb.Ecommerce.Products.ProductCollection.LoadProductCategoryValues()
   at Dynamicweb.Ecommerce.Frontend.Frontend.ListProducts(ProductCollection products, String groupsIdent, Boolean hasBeenSorted)
   at Dynamicweb.Ecommerce.Frontend.Frontend.List(String groups)
   at Dynamicweb.Ecommerce.Frontend.Frontend.EcomRender()
   at Dynamicweb.Ecommerce.Frontend.Frontend.GetContent()
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)