An unknown exception was received. The formatter threw an exception while trying to deserialize the message: There was an error while trying to deserialize parameter http://tempuri.org/:nodes. The InnerException message was 'Error in line 1 position 2125. Element 'http://schemas.datacontract.org/2004/07/MessageContracts:value' contains data from a type that maps to the name 'http://schemas.datacontract.org/2004/07/MessageContracts:Klass2'. The deserializer has no knowledge of any type that maps to this name. Consider using a DataContractResolver or add the type corresponding to 'Klass2' to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding it to the list of known types passed to DataContractSerializer.'.  Please see InnerException for more details.

<startup>
  <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5"/>
</startup>