Null Reference Exception with ComboBox ItemSelection (System.Windows.Controls.Primitives.Popup.OnWindowResize)

Hi,

I am using VS2010 and framework 3.5 sp1.

In my WPF application, when i select an item in my combobox its throwing nullreference exception.

and the stack shows

   002DE1BC 70047A41 PresentationFramework_ni!System.Windows.Controls.Primitives.Popup.OnWindowResize(System.Object, System.Windows.AutoResizedEventArgs)+0x29
    002DE1E4 7066412F PresentationCore_ni!System.Windows.Interop.HwndSource.Resize(System.Windows.Size)+0xdf
    002DE248 70636B3E PresentationCore_ni!System.Windows.Interop.HwndSource.OnLayoutUpdated(System.Object, System.EventArgs)+0xfe
    002DE2AC 70636978 PresentationCore_ni!System.Windows.ContextLayoutManager.fireLayoutUpdateEvent()+0xb8
    002DE2E4 70636401 PresentationCore_ni!System.Windows.ContextLayoutManager.UpdateLayout()+0x641
    002DE3EC 7063C6B9 PresentationCore_ni!System.Windows.ContextLayoutManager.UpdateLayoutCallback(System.Object)+0x19
    002DE3F0 7063C690 PresentationCore_ni!System.Windows.Media.MediaContext+InvokeOnRenderCallback.DoWork()+0x10
    002DE3F4 7063C637 PresentationCore_ni!System.Windows.Media.MediaContext.FireInvokeOnRenderCallbacks()+0x97
    002DE410 7063BFA0 PresentationCore_ni!System.Windows.Media.MediaContext.RenderMessageHandlerCore(System.Object)+0x80
    002DE45C 7063BEFB PresentationCore_ni!System.Windows.Media.MediaContext.RenderMessageHandler(System.Object)+0x2b
    002DE488 73B864AA WindowsBase_ni!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate, System.Object, Boolean)+0x8a
    002DE4AC 73B86401 WindowsBase_ni!System.Windows.Threading.ExceptionWrapper.TryCatchWhen(System.Object, System.Delegate, System.Object, Boolean, System.Delegate)+0xb1
    002DE4F4 73B84504 WindowsBase_ni!System.Windows.Threading.Dispatcher.WrappedInvoke(System.Delegate, System.Object, Boolean, System.Delegate)+0x44
    002DE514 73B893DD WindowsBase_ni!System.Windows.Threading.DispatcherOperation.InvokeImpl()+0x5d
    002DE540 73B89368 WindowsBase_ni!System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(System.Object)+0x38
    002DE548 719D5731 mscorlib_ni!System.Threading.ExecutionContext.runTryCode(System.Object)+0x51
    002DE9DC 719D5627 mscorlib_ni!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object)+0x67
    002DE9F8 719C0255 mscorlib_ni!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object)+0x45
    002DEA10 73B892A3 WindowsBase_ni!System.Windows.Threading.DispatcherOperation.Invoke()+0x63
    002DEA48 73B83BA7 WindowsBase_ni!System.Windows.Threading.Dispatcher.ProcessQueue()+0x127
    002DEB24 73B83E93 WindowsBase_ni!System.Windows.Threading.Dispatcher.WndProcHook(IntPtr, Int32, IntPtr, IntPtr, Boolean ByRef)+0x63
    002DEB70 73B8668E WindowsBase_ni!MS.Win32.HwndWrapper.WndProc(IntPtr, Int32, IntPtr, IntPtr, Boolean ByRef)+0xbe
    002DEBBC 73B865BA WindowsBase_ni!MS.Win32.HwndSubclass.DispatcherCallbackOperation(System.Object)+0x7a
    002DEBCC 73B864AA WindowsBase_ni!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate, System.Object, Boolean)+0x8a
    002DEBF0 73B8639A WindowsBase_ni!System.Windows.Threading.ExceptionWrapper.TryCatchWhen(System.Object, System.Delegate, System.Object, Boolean, System.Delegate)+0x4a
    002DEC38 73B84504 WindowsBase_ni!System.Windows.Threading.Dispatcher.WrappedInvoke(System.Delegate, System.Object, Boolean, System.Delegate)+0x44
    002DEC58 73B83661 WindowsBase_ni!System.Windows.Threading.Dispatcher.InvokeImpl(System.Windows.Threading.DispatcherPriority, System.TimeSpan, System.Delegate, System.Object, Boolean)+0x91
    002DEC9C 73B835B0 WindowsBase_ni!System.Windows.Threading.Dispatcher.Invoke(System.Windows.Threading.DispatcherPriority, System.Delegate, System.Object)+0x40
    002DECC0 73B85CFC WindowsBase_ni!MS.Win32.HwndSubclass.SubclassWndProc(IntPtr, Int32, IntPtr, IntPtr)+0xdc
    002DEE58 73B83CA4 WindowsBase_ni!System.Windows.Threading.Dispatcher.PushFrameImpl(System.Windows.Threading.DispatcherFrame)+0xc4
    002DEEA8 73B83379 WindowsBase_ni!System.Windows.Threading.Dispatcher.PushFrame(System.Windows.Threading.DispatcherFrame)+0x49
    002DEEB4 73B8331C WindowsBase_ni!System.Windows.Threading.Dispatcher.Run()+0x4c
    002DEEC0 6F86E37E PresentationFramework_ni!System.Windows.Application.RunDispatcher(System.Object)+0x1e
    002DEECC 6F86D67F PresentationFramework_ni!System.Windows.Application.RunInternal(System.Windows.Window)+0x6f
    002DEEF0 6F8549D6 PresentationFramework_ni!System.Windows.Application.Run(System.Windows.Window)+0x26
    002DEF00 6F854999 PresentationFramework_ni!System.Windows.Application.Run()+0x19

The code snipped is below.

<ComboBox Width="200"
         x:Name="cmbEntityTypes"
         SelectionChanged="cmbEntityTypes_SelectionChanged"
         ItemsSource="{Binding ElementName=thisUserControl, Path=EntityTypes}">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock>
<TextBlock.Text>
<MultiBinding Converter="{StaticResource LocalizationPrefixMultiConverter}"
             ConverterParameter="EntityCombo">
<Binding Path="EntityDisplayName" />
<Binding Path="CurrentCulture"
        Source="{x:Static l:LocalizationManagers.Instance}" />
<Binding Source="ClientSearch" />
</MultiBinding>
</TextBlock.Text>
</TextBlock>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>

I already saw a post related to this kind of error, but was not useful

Thanks

kiran