Error message when creating discount

When creating a discount in episerver back office I recieve the following error: Content with id '11663 is of type 'Castle.Proxies.SalesCampaignProxy' which does not inherit required type 'EPiServer.Commerce.Catalog.ContentTypes.CatalogContentBase

The discount is anyway created and works as expected. When I decompile SalesCampaign I can se that it inherits from BasicContent. 

Has someone encountered this error before?

Thanks in advance.