Vista - IAddChild and XAML serialization process ??

Hello

I try to use xaml serializer framework to save in .xaml file my own
hierarchical graph of object.

The first step is done : I create my own file with something like this :

<Root
xmlns="clr-namespace:myNameSpace;assembly=MyAssembly">
<Structure ...>
<SimpleText ... />
</Structure>
</Root>

with a simple call like this :

outStream = new System.IO.FileStream(@"c:\temp\essai.xaml",
System.IO.FileMode.Create);
using (outStream)
{
System.Windows.Markup.XamlWriter.Save(rootInstance,
outStream);
}

BUT when I want to reverse the process (Create a RootInstance from xaml
file) with a call like this :

System.IO.FileStream inStream = new
System.IO.FileStream(@"c:\temp\essai.xaml",
System.IO.FileMode.Open);
using (inStream)
{
return
(Root)System.Windows.Markup.XamlReader.Load(inStream);
}

Root is created
Structure is created
SimpleText is created
BUT i have after this, an exception like "SimpleText can be added in
Structure" occurs !!

Structure and Root supports IEnumerable and IAddChild interface !!

I don't know what I forgot somewhere ????

could you help me

thanks a lot for your help !