Clearing Object in Frame

[Oliver]

i using Frame Navigate in Master page. from code behind.

Private Sub F_ItemDoubleClick(ByVal sender As Object, ByVal e As Telerik.Windows.RadRoutedEventArgs) Handles F.ItemDoubleClick


    Select Case CType(e.Source, RadTreeViewItem).Tag
        Case "form1"
            ContentFrame.Navigate(New Uri("/Views/vForm1.xaml", UriKind.Relative))
        Case "form2"
            Helpers.MyDocType = "form2"
            ContentFrame.Navigate(New Uri("/Views/vFormTwo.xaml", UriKind.Relative))
        Case "form3"
            Helpers.MyDocType = "form3"
            ContentFrame.Navigate(New Uri("/Views/vFormTwo.xaml", UriKind.Relative))
        Case Else

    End Select

End Sub

but i have a problem. after click form 2 , then not working form 3!
i want clear cashe and fixed my problem.
please help me...