Given the following classes:

public class C

{ public int _id; public N n; }

public class N

{ public int x; }

the following code results in an InvalidOperationException:

var json = "

{ '_id' : 1, n : 'should be a document, not a string' }

";
BsonSerializer.Deserialize<C>(json);

The error message should be more specific, identifying which property of which class couldn't be deserialized.