Dispatcher.Run() throws a Win32Exception

I have a legacy modal dialog that I need to present from a windows WPF/C# application. It generally works well but under the specific circumstance of a published application in RDS if the user waits for a few minutes between the main application and then invoking the dialog it will crash with a rather cryptic error.

I would like to know how to get a list of messages that the dispatcher is running: if I could analyse the messages being processed then I could have a shot at understanding the underlying problem.

The actual exception is a Win32Exception. The Message is "The system cannot find the file specified". The HResult is x80004005. 

The complete error text is

System.ComponentModel.Win32Exception (0x80004005): The system cannot find the file specified
at MS.Win32.UnsafeNativeMethods.GetWindowText(HandleRef hWnd, StringBuilder lpString, Int32 nMaxCount)
at System.Windows.Automation.Peers.WindowAutomationPeer.GetNameCore()
at System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
at System.Windows.Automation.Peers.AutomationPeer.UpdatePeer(Object arg)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
at System.Windows.Threading.DispatcherOperation.InvokeImpl()
at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Windows.Threading.DispatcherOperation.Invoke()
at System.Windows.Threading.Dispatcher.ProcessQueue()
at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndSubclass.Disp

try
{
    Dispatcher.Run();
}
catch (Win32Exception e)
{
    ExceptionHandler.ShowException(e, e.Message );
}