I would suggest upgrading your Xamarin.Android version and your current dlls to the new "Xamarin" versions.
EX:
<Reference Include="Xamarin.Android.Support.v4">
<HintPath>Components\xamandroidsupportv7appcompat-7.18.0\lib\android\Xamarin.Android.Support.v4.dll</HintPath>
</Reference>
You can add these by right-clicking the components folder and searching for support libraries.
Here's v4: https://components.xamarin.com/view/xamandroidsupportv4-18