Type "%1!s!.%2!s!" is marked for native serialization, but field "%3!s!" of type "%4!s!.%5!s!" is of type "%6!s!.%7!s!" which ...

Type "%1!s!.%2!s!" is marked for native serialization, but field "%3!s!" of type "%4!s!.%5!s!" is of type "%6!s!.%7!s!" which is a non-value type. Native serialization types can only have fields of blittable types. If you wish to have a field of any other type, consider using different kind of serialization format, such as User Defined Serialization.