I have a new Xamarin Forms solution setup with a PCL, an iOS app (which builds fine), and an Android project. The Android project is up to date with the latest Nuget packages fo
Check your android sdk manager and uninstall all Android SDK Build Tools except for the lastest and greatest
Close Visual Studio and Delete Everything in this folder and C:\Users\YOURUSER\AppData\Local\Xamarin\
Reopen Project And Rebuild Solution and visual Studio will re-download files needed back in that folder and you should be set to go