Rebuilding the Outlook Interop Assembly
 
The preferred means of referencing Outlook is with an Outlook Primary Interop _
  Assembly (PIA). The Outlook PIA is only available for Outlook 2002 and Office _
  XP. If you are targeting both Outlook 2000 and 2002, you will have to rebuild _
  the Outlook Assembly used for COM Interop. If you plan to build an _
  event-aware application, you must rebuild Interop.Outlook.dll. The following _
  article applies to Excel Events. You can use the steps outlined in this _
  article to modify Interop.Outlook.IL and rebuild Interop.Outlook.dll.
 
[URL=http://support.microsoft.com/?kbid=316653]PRB: Error Using WithEvents or _
  Delegates to Handle Excel Events from Visual Basic .NET or Visual C# .NET ( _
  Q316653)[/URL]
 
The sequence of steps to rebuild Interop.Outlook.dll is as follows:
 
1. Save and close your Visual Studio .NET project. 
 
2. Open a Visual Studio .NET command prompt and change the directory to the _
  output
   Directory of your project (for example, project name \bin for a Visual Basic _
   project or 
   project name \bin\release for a C# project). 
 
3. Use Ildasm.exe to extract the intermediate language from the Outlook interop 
   assembly, as follows: 
   ildasm.exe /source Interop.Outlook.dll /output=Interop.Outlook.il  
 
4. Open Interop.Outlook.il in a text editor such as WordPad and search for _
  occurrences 
   of "_SinkHelper". Change the access privileges of the _SinkHelper classes _
   from 
   Private to Public, and then save and close Interop.Outlook.il. 
 
5. Open your project in Visual Studio .NET. 
 
6. In Visual Studio .NET Solution Explorer, right-click Outlook in the list of _
  project 
   references and then click Properties . Change the Copy Local property to _
   False . 
 
   IMPORTANT : This step is required. If you do not set the Copy Local _
     property of 
   the reference to False , Visual Studio .NET regenerates the interop assembly _
   when 
   you compile the project. 
 
7. At the Visual Studio .NET command prompt, use Ilasm.exe with the /dll switch _
  to 
   recompile the intermediate language file into an interop assembly, as _
   follows: 
   ilasm.exe /dll Interop.Outlook.il /output=Interop.Outlook.dll