I just installed the Xamarin Stable Release (Sept 13, 2016). The Xamarin update appeared to go well, but following the update and reboot, the compiler complained about version conflicts of some sort. After Googling for a solution and finding old posts, I checked for updates and found a Visual Studio 2015 update that I applied. After reboot, the compiler was still complaining about version conflicts, so I ran Android SDK Manager and saw a few updates. I opted to install the updates and that's where the problems really began. The updates failed, complaining about an inability to rename/move the ...\tools folder. Visual Studio 2015 was closed, so I tried disabling Windows Defender, but no luck. The SDK Manager failed in such a way that after closing Android SDK Manager, it would not run again. I manually reinstalled the latest Android SDK Manager and am now in the process of re-installing all of my SDKs. At this point, if this doesn't work, I'm going to revert to the full system backup that I did (fortunately) prior to starting this latest update.