title: Can't compile Xamarin project, four errors when I compile
body: <p>This is a mobile app written in Xamarin. Latest version of Xamarin. Won't compile the android project.  iOS compiles fine.  Installed latest 'everything'.  Tried deleting obj/bin, packages and restoring.  </p>
  
  <p>/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Aapt2.targets(154,3): error APT2062: failed linking references.</p>
  
  <p>/Users/userX/code/work/example-app/Example.Services.Client.Forms.Droid/obj/Debug/lp/1/jl/res/values/values.xml(0,0): Error APT2260: style attribute 'attr/cardBackgroundColor (aka Example.Services.Client.Forms.Droid:attr/cardBackgroundColor)' not found. (APT2260)</p>
  
  <p>/Users/userX/code/work/example-app/Example.Services.Client.Forms.Droid/obj/Debug/lp/1/jl/res/values/values.xml(0,0): Error APT2260: style attribute 'attr/cardElevation (aka Example.Services.Client.Forms.Droid:attr/cardElevation)' not found. (APT2260) (Example.Services.Client.Forms.Droid)</p>
  
  <p>/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Aapt2.targets(3,3): Error APT2260: resource style/CardView (aka Example.Services.Client.Forms.Droid:style/CardView) not found. (APT2260) (Example.Services.Client.Forms.Droid)</p>