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_GroupRelationsByParentId(String theParentId)
   at Dynamicweb.Ecommerce.Products.Group.get_Subgroups()
   at Dynamicweb.Ecommerce.Extensibility.Controls.ProductsAndGroupsHandler.GetGroupsAndChildGroups(IEnumerable`1 groups)
   at Dynamicweb.Ecommerce.Frontend.ProductCatalogSettings.SetGroups(IEnumerable`1 groups)
   at Dynamicweb.Ecommerce.Frontend.Frontend.EcomRender()
   at Dynamicweb.Ecommerce.Frontend.Frontend.GetContent()
   at Dynamicweb.Frontend.Content.GetModuleOutput(Paragraph paragraph, PageView pageview)

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