Inheriting from Pair

[Charles]

I assumed I could inherit from Pair in order to create a friendly interface
to users, while gaining the benefits of the Pair class for saving to the
ViewState
E.g.

[Serializable()]
public class FriendlyPair: Pair
{
public string String1
{
get {return (string)First;}
set {First = value;}
}
public string String2
{
get {return (string)Second;}
set {Second= value;}
}
}

However, when I try to save it to the ViewState, I get this message:
The type 'FriendlyPair' must be marked as Serializable or have a
TypeConverter other than ReferenceConverter to be put in viewstate

It seems to me that it surely is marked Serializable.

The same message occurs even with an explicit conversion:

protected override object SaveViewState()
{
return (Pair)friendlyPair;
}

Why don't I inherit all the benefits of the Pair class?