Because of the pain you are experiencing today, I avoid them. I do not avoid them because they are ugly. I believe it is possible to pass the fully qualified name using the Namespace. Do not use Quotations. Quotes will indicate to the DoCmd Paramater that you are passing a String Argument. Pass the Object, instead.
You will need to pass the name of the actual Navigation Control. This is hard to find. The way I remember it, when using the Wizard to create the form, You have the Form Name and then there is the control that is the Navigation thing. This resides just inside the form. This Navigation Control has all sorts of stuff inside of it. Maybe there are some Tabs you need to identify. Your Form Object may be contained within one of those.
Code:
[Forms]![mainform]![CorrectNavigationName ].[Form]!tbStart