In visual studio I am creating an addin, in the addin_startup I am setting an Outlook application to
app = (Microsoft.Office.Interop.Outlook.ApplicationClas
I don't know why you have your exact issue, I'd assume one or more parameters is incorrect but not sure since I've never done it the way you're trying to do it.
I'd suggest looking at the following article for a complete sample using somewhat different code, that you might be able to reuse in your code: HOW TO: Run Office Macros by Using Automation from Visual C# .NET