title: Excel Add-In throws SHException
body: <p>I have an excel addin, written in C#, .NET 35 SP1
  using ExcelDNA, NetOffice 
  Occasionally clients reported my add-in disappear from Excel, I check it is in disabled addin list, 
  I enable it and it works again. 
  I checked my log and saw SHException. Not sure what causes and how to fix it.  thanks </p>
  
  <p>One thing I notice client has several other addins in Excel.  Also has .NET 1.1, .NET 2.0, .NET 3.0, NET 35 SP1 </p>
  
  <pre><code>2012-01-31 07:10:12,672 [1] ERROR Shared.Helper [(null)] - Name:SEHException
  Message:External component has thrown an exception.
  Target:Int32 IntGetMessageW(System.Windows.Interop.MSG ByRef, System.Runtime.InteropServices.HandleRef, Int32, Int32)
  Stack:   at MS.Win32.UnsafeNativeMethods.IntGetMessageW(MSG&amp; msg, HandleRef hWnd, Int32 uMsgFilterMin, Int32 uMsgFilterMax)
     at MS.Win32.UnsafeNativeMethods.GetMessageW(MSG&amp; msg, HandleRef hWnd, Int32 uMsgFilterMin, Int32 uMsgFilterMax)
     at System.Windows.Threading.Dispatcher.GetMessage(MSG&amp; msg, IntPtr hwnd, Int32 minMessage, Int32 maxMessage)
     at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
     at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
     at System.Windows.Window.ShowHelper(Object booleanBox)
     at System.Windows.Window.Show()
     at System.Windows.Window.ShowDialog()
     at ExcelAddIn.Connect.ShowRefreshUI(Boolean checkForSettings, Boolean isRefreshAll)
  </code></pre>