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

System.ArgumentException: An item with the same key has already been added. Key: CustomField_CustomIndgangsspaending
   at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)
   at Dynamicweb.Ecommerce.ProductCatalog.ViewEngine.CollectFacetFieldsToBeRemoved(Dictionary`2 facetFieldsToBeRemoved, List`1 groupFacets)
   at Dynamicweb.Ecommerce.ProductCatalog.ViewEngine.CreateView(IEnumerable`1 facetGroups, IDictionary`2 facetGroupResults, IDictionary`2 facetParameters, IEnumerable`1 queryParameters, Boolean showFacetOptionsWithNoResults)
   at Dynamicweb.Ecommerce.Indexing.ProductQueryHelper.GetProductsAutoIdsFromIndexQuery(IQuery query, ProductCatalogSettings settings, QuerySettings querySettings, IEnumerable`1& facetViewModel, IEnumerable`1& spellCheckerResult)
   at Dynamicweb.Ecommerce.ProductCatalog.ProductCatalogFrontend.RenderProductList(ProductCatalogSettings settings, QuerySettings querySettings, IQuery query, String groupId, Boolean feed, Boolean compare)
   at Dynamicweb.Ecommerce.ProductCatalog.ProductCatalogFrontend.GetModuleContent()
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)