SharePoint Client Object Model - Problem adding Item to List

Question

The VB code below works in a stand-alone Silverlight app to add new items to a pre-existing list, but when I include it in a larger app it doesn't.

The only difference I can see is that with the standalone app MainPage.xaml.vb has INHERITS USERCONTROL and with the larger app Page2.xaml.vb has INHERITS PAGE.

Would this make a difference?

Thanks,

JT

Imports Microsoft.SharePoint.Client
Partial Public Class MainPage
    Inherits UserControl

    Public Sub New()
        InitializeComponent()
    End Sub

Private Sub onAddSucceeded(ByVal sender As Object, ByVal args As ClientRequestSucceededEventArgs)
    MessageBox.Show("Person Added")
    Dim updateUI As UpdateUIMethod = AddressOf DisplayInfo
    Me.Dispatcher.BeginInvoke(updateUI)
End Sub

Private Sub onAddFailed(ByVal sender As Object, ByVal args As ClientRequestFailedEventArgs)
    MessageBox.Show("Epic Fail!" & args.Message & vbLf & args.StackTrace)
End Sub

Private Sub DisplayInfo()
    MessageBox.Show("Finished")
End Sub


Private Delegate Sub UpdateUIMethod()

Private Sub Button1_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles Button1.Click
    Dim clientContext As ClientContext = clientContext.Current
    Dim oList As List = clientContext.Web.Lists.GetByTitle("pfa")

    Dim itemCreateInfo As New ListItemCreationInformation()
    Dim oListItem As ListItem = oList.AddItem(itemCreateInfo)
    oListItem("FullName") = TextBox1.Text
    oListItem("Role") = TextBox2.Text
    oListItem("Length") = TextBox3.Text

    oListItem.Update()

    clientContext.ExecuteQueryAsync(AddressOf OnAddSucceeded, AddressOf OnAddFailed)
End Sub

End Class