I tried to make a simple Forms app and it worked until I added an external .xaml file, then wanted to return an instance of that class instead of the default content of GetMainPage. The compiler can't find that class, but the code completion can - this is the case whether I refer to the namespace or just the class name (they are both in the same namespace so the class name should be all that is required), the same is the case if I add a new class that derives from page but otherwise does nothing and if I add a new class that does nothing at all (ie the template that gets created when you create a new empty class).
So I figured no big deal I can refer to the xaml backed class directly in my Android activity. No dice, it also pretends the class does not exist.
Finally I tried refreshing the package manager and it came up with this weird error:
Access to path 'Xamarin.Forms.Build.Tasks.dll' was refused.
I am admin on this win 8 computer and this error is persistent across Xamarin restarts.