A business partner using Visual Studio 2005 developing workflow components emailed me through here, so I figured I'd post the answer.
Problem:
When you use one of the iMotion project item templates in Visual Studio 2005, it will product the wrong language code. A C# project will create VB.NET code and vice versa.
Cause:
There is a bug in the installer where the registry keys used to install templates into Visual Studio are reversed (causing the language switch).
Solution:
Log onto DevHelp (http://devhelp.globeranger.com) and go to Support then Utilities for the iMotion Platform. The (current) first download in the list is a registry file you can use to fix the problem. Download the file and import it into your registry.