I had the same error before. Just open the package manager and delete/uninstall everything for Android M (API 22 MNC Preview). Marshmallow is already out anyway.
You may have to restart Android Studio afterward cause it caches that check.
The M release has been removed from the packages for some reason after the Marshmallow release and I think that error means he can’t find the upgrade to those images. When you wipe them out it stop complaining and you do not see them anymore on the list of packages.
In Android Studio:
- Open SDK Manager. To do that, go to
Settings -> Appearance & Behavior -> System Settings -> Android SDK - Make sure you are in the
SDK Platformtab - Uncheck Android M (API 22, MNC Preview)
- Click “OK”