WCF serialization - namespace? or KnownType/interface problem?

hello

I'm running into Serialization problem with WCF again and I'm not sure if it arise from namespace problem or KnownType/interface...

Code:

---

[DataContract(Name = "Person")]
public class Person : IHierachicalPropOwner
{
...
IHierarchProp HierarchicalProp
{
  get {...}
  set {...}
}
...
}

public interface IHierarchicalPropOwner
{
  ...
  IHierarchProp HierarchicalProp;
  ...
}

[KnownType(typeof(Person))] // Because List<IHierarchicalPropOwner> is actually List<Person>, I include Person as KnownType as well.
[DataContract()]
public class HierarchicalProp : IHierarchProp
{
  ...
  [DataMember()]
  public List<IHierarchicalPropOwner> Parents
  {
      get ...
      set ...
  }
  [DataMember()]
  public List<IHierarchicalPropOwner> Children
  {
      get ...
      set ...
  }
  ...
}

---

Now all seems good initially up until I added Parents/Children (from IHierarchProp) - i.e. Person class serialize/deserialize successfully BEFORE I added Parents/Children (which are also of type Person) ... I checked SrvTraceViewer, the message was:

Code:

---

Type 'PersonProxy84be8e34abd44adf9c275dce3b694daf' cannot have DataContractAttribute attribute Namespace set to null.

---

I don't know why I must add a namespace but I did change Person's DataContract attrib:

Code:

---

[DataContract(Name = "Person", Namespace="Util")]
public class Person : IHierachicalPropOwner
{
...
}

---

I then fired it up again, and ran into a different error message

Code:

---

There was an error while trying to serialize parameter http://tempuri.org/:AuthenticateUserResult. The InnerException message was 'Type 'PersonProxy9ae63f0c5e1b403881f64f08908cf759' with data contract name 'Person:Util' is not expected. Add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.'.  Please see InnerException for more details

---

Adding to service contract ServiceKnownType didn't help it but I made sure I have...

Code:

---

[ServiceKnownType(typeof(Person))]

---

Now I was suspecting perhaps DataContractSerializer need Person's namespace as specified in [DataContract] namespace attib be same as that of "Service Reference" when you "Add Service Reference" from Visual Studio (you set service namespace at that time). So I go ahead and make the change:

Code:

---

[DataContract(Name = "Person", Namespace="SecurityServiceRef")]
public class Person : IHierachicalPropOwner
{
...
}

---

The error did NOT go away,

Code:

---

There was an error while trying to serialize parameter http://tempuri.org/:AuthenticateUserResult. The InnerException message was 'Type 'PersonProxyebe18eee73cd41db908097f0886b787e' with data contract name 'Person:ServiceServiceRef' is not expected. Add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.'.  Please see InnerException for more details.

---

Any idea? Many Thanks!

REF:
http://msdn.microsoft.com/en-us/library/ms730167.aspxvv