VS2008 WinForms Designer: 'Could not load file or assembly' upon startup

Question

I have a WinForms application that references one of my DLLs Mvc.dll via a file reference. The main application form uses a user control SimpleWizard that in turn uses a user control called SimpleWizardList, which in turn references Mvc.dll in its constructor.

When starting VS2008, the designer complains Could not load file or assembly 'Mvc.dll' and shows a callstack:

at SimpleWizardList..ctor()
at SimpleWizard.InitializeComponent()
at SimpleWizard..ctor()

If I close the design window, clean and rebuild the app, the designer re-opens just fine.

public SimpleWizardList()
{
    InitializeComponent();

    // ChangeRequestEvents is defined in Mvc.dll
    changeRequestedEvents = new ChangeRequestEvents(this);
}

I can always recover by doing a clean and rebuild, but this is a bit annoying.

Any thoughts on why the error is happening or how to prevent it?