“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

Change this:

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

to this:

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