Could not resolve id ‘:@Hidden’ to a model item

In Lightswitch server project change property set bydefault false to true.and project gets failed. The key field ContactId [Guid] is required and 'Display by Default: false' but if you change this then the 'Contact.lsml' overrides metadata is corrupted and can only be manually corrected. This XML needs deleting.   <KeyProperty.Attributes> <Proxy Target="ServiceInterface:Contact/Properties[ContactId]" /> <DiscardFromCollection PropertyName="Attributes" Item=":@Hidden" /> In html client project open property folder and remove this added field property and reload server [...]