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.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.d__42.MoveNext()
   at Dynamicweb.Ecommerce.Frontend.Renderer.RenderProductCategories(Product product, Template template, String loopName, Lazy`1 categoryFieldSortings, RenderingContext renderingContext)
   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.RenderProducts(ProductCollection products, Template parentTemplate, String loopName, Int32 loopCounter, Boolean renderRelatedProducts, Boolean renderRelatedLists, Boolean isRecursive, RenderingContext renderingContext)
   at Dynamicweb.Ecommerce.Frontend.Renderer.RenderProductRelatedGroups(RenderingContext renderingContext, Product product, Template parentTemplate, String loopName)
   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.EcomRender()
   at Dynamicweb.Ecommerce.Frontend.Frontend.GetContent()
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)