An unhandled exception of type 'System.NullReferenceException' occurred in Unknown Module.
When loading large shape files you can sometimes get the above error message. This happens under .NET when running in debug mode from Visual Studio.
Microsoft (official denied) bug in Visual Studio 2003 and 2002
In Visual Studio simply click "Continue", and everything will continue.
If compiled in Release mode, and run as a stand alone application, this should not happen.