I was working on an Android project using Xamarin in Visual Studio 2012. I recently upgraded from an HDD to a SSD so I reinstalled Windows and all of my programs.
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Obviously the OP figured out the issue to their problem but I still wanted to post an answer relating to an issue I had with the same error message. I am using Visual Studio (within Parallels) and attempting to debug the app on a Xamarin Android Player instance (which is running on my Mac).
I kept getting this error and realized that a different, more helpful, error message was showing up in the Build Output saying that I was not supporting the correct architecture.
Heading into the Android Project Properties -> Android Options -> Advanced -> and checking x86
finally allowed my to successfully deploy to the Xamarin Android Player.