Dynamic load workspaces

   Hello Cocktail colleague's,

I’m writing my first cocktail Silverlight (SL5) application en getting familiair with MEF.
So, I’m new to this.

I’m trying to dynamically load a IWorkspace ViewModel from a separate XAP file. I’m using the example found in the documentation. 
On the main SL application (the one loading a SSHBizzOrganisation module) I have the following code.
Basically copied from the example.

[Import("MainViewModel", AllowRecomposition = true, AllowDefault = true)] 
public ExportFactory<IWorkspace> OrganisationModuleFactory { get; set; }

private IEnumerable<INotifyCompleted> ShowOrderDetail(OrganisationModuleMessage message) {

// Let's make sure the xap that contains the OrderEditor is loaded. 
// Only the first call will load the xap, subsequent calls don't do anything. 
yield return Composition.AddXapAsync("SSHBizzOrganisation.SL.xap");
// Now we can access the OrderEditorFactory. MEF recomposed this instance 
// and provided us with an OrderEditorFactory. 
var editor = OrganisationModuleFactory.CreateExport().Value;
var handler = editor as IHandle<OrganisationModuleMessage>; 
if(handler != null) handler.Handle(message); 
}

When I run this, the AddXapAsync(..) call is working fine.
But the ‘OrganisationModuleFactory’ property is always null.
I’m sure I forgetting something here of within the module implementation.
The SSHBizzOrganisation module looks like this:

namespace SSHBizzOrganisation.ViewModels
{

[Export(typeof(IWorkspace))]
public class MainViewModel : Screen, IWorkspace, IDiscoverableViewModel
{

public MainViewModel()
{ // ReSharper disable DoNotCallOverridableMethodsInConstructor
DisplayName = "Desktop";
// ReSharper restore DoNotCallOverridableMethodsInConstructor
}

I have read some of the forum posts, but I probably missing some basic understanding.
It’s not clear to me if I should use the PartFactory implementation or just use the [Export] attribute like I’ve done above. 
I have tried both.

Hope some can point me in the right direction.
Peter