title: Missing Android 3.1 SDK in Visual Studio 2013 using Xamarin
body: <p>So I just reinstalled the lastest version of Xamarin after a clean install of my laptop.  There were no errors during the Xamarin install, so everything seemed okay.  However, I went to open an existing project based on Android 3.1 (API 12) and got the following error when I compiled:</p>
  
  <p>Unsupported or invalid $(TargetFrameworkVersion) value of 'v3.1'. Please update your Project Options.</p>
  
  <p>Checked out my project properties and found that both the Compile and Target Android version combos were blank.  I have several versions listed in the combos, but v3.1 (API 12) is nowhere to be found.  When I look in the Android SDK Manager, it shows that Android 3.1 (API 12) is installed.  Anyone know why it would be missing in Visual Studio/Xamarin?</p>
  
  <p><img src="https://i.stack.imgur.com/MSTYl.png" alt="Android SDK Manager"></p>