Instances of DomainClass '{0}' cannot be serialized as a moniker. A DomainClass can be serialized as a moniker only if 1) ...

Instances of DomainClass '{0}' cannot be serialized as a moniker.
A DomainClass can be serialized as a moniker only if 
1) it has a defined/inherited DomainProperty marked as IsMonikerKey=true, or 
2) it is marked/inherited with SerializeId=true.