Error Message if I add Xamarin.Mobile package

Hello,
I get the following error messing if I try to add Xamarin.Mobile package :

Could not install package 'xamstore-xamarin.mobile 0.7.1'. You are trying to install this package into a project that targets 'portable-net45+win+wp80+MonoAndroid10+MonoTouch10', but the package does not contain any assembly references or content files that are compatible with that framework. For more information, contact the package author.

Can anyone help ?

Best regards
Axel