What you should do here: dump the outer ScrollView, you don't need it. Only use a ListView, and add the button to the ListView, using .addFooter(), that's the easiest way. This way your button'll appear as a list element, but you don't have to mess around with a custom adapter.
You can't put a ListView inside a ScrollView. Of GridView, or whatever View that handles scrolling on the same axis as the ScrollView does. That way the framework wouldn't know which View should handle the scrolling event. This layout won't produce an error when you compile it, but it won't work properly.