Android keyword not recognized

Hello,

This is my configuration :

VS 2015 with Xamarin
Android tools, API 22 and 23 with all android extras up to date
Project with forms 2.0.0.6490 and all nugets packages up to date.

My app is with MVVM and a navigationService.

Any Android keyword in the using part is unknow, so my Android project isn't working.

Some pictures :
https://gyazo.com/582d1dfcc034200d9d5921549d76267d

https://gyazo.com/26bdbfa0c3a890b790fa4049f2cf8c78

https://gyazo.com/56b42e67035bf5aaf42c6bd53f9a1ab0
2922 errors for this file, with unknow Resource.Animation

I try to change every parameters, to erase the file, but after rebuild, it's always impossible to compile the project.

Could you help me ?

Regards