I received the following bug report from a customer:

System.IO.FileNotFoundException: File or assembly name Microsoft.mshtml, or one of its dependencies, was not found.

My MZ-Tools add-in references this component. Actually it doesn’t use it  (it was for future HTML/ASP.NET support) but that doesn’t matter. AFAIK, that component was installed by every installation of Visual Studio, because it is used for the ASP.NET/HTML designers (which until VS 2008 were IE-based). How could be that the customer didn’t have it?

It turned out that the customer was using Visual Studio .NET 2003 and that he installed only Visual C++, neither VB.NET nor C#. It seems that Visual C++ 2003 doesn’t use that component, and as soon as he installed VB.NET, the component was installed…

BTW, it seems that each time that I think about dropping support for VS.NET 2003 and concentrating only in VS 2005, 2008 and 2010 with .NET 2.0, I receive an e-mail from someone that happens to use VS.NET 2003… definitely developers of commercial add-ins need to support old versions of Visual Studio for many years….