The C# API for Inventor is just a little bit different than the VBA and Visual Basic API. I would love to see better documentation of this, or even a separate API reference for C# users. Visual Basic is no longer being developed by Microsoft, and with the new features being included in C# it is a more logical choice.
Example: The VB.NET API call for getting a parameter's units is UserParameter.Units, where the C# call is UserParameter.get_Units().