Android - An element with the same key already exists in the dictionary

When I try to deploy my Xamarin.Forms app to my emulator I get the following deployment error message.

An element with the same key already exists in the dictionary

I spent a couple of hours removing/adding references (apparently a solution), then I tried playing with the project options. I unchecked 'Use Shared Mono Runtime', and now I get a slightly different error, this time when building the package

/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets: Error: Error executing task BuildApk: An element with the same key already exists in the dictionary. (YooDooForms.Android)

Any ideas anyone ? Ive got the bare bones of my Xamarin.Forms IOS app finally deploying, but now the Android deployment has become equally problematic and obscure in its issues.

Thanks