“Type not expected”, using DataContractSerializer - but it's just a simple class, no funny stuff?

Question

I\'m refactoring my XML-serialization, and figured I\'d try the DataContractSerializer. Everything runs smoothly, until it needs to serialize this class:

Answer 1

It is like as @Leon suggested but with the fix from @Bryan, the 'KnownTypeAttribute' should be on the base class, so it should be like this:

[DataContract(Name="DataFelt")]
[KnownType(typeof(somenamespace.Konstant))]
public class DataFelt

and in the Subclass:

[DataContract(Name="Konstant")]
public class Konstant : DataFelt