XML : C# WP error: Project must have either AppxManifest

I tried adding a new WP User Control on my project. I ran to this error: Project must have either AppxManifest item or Content item with name 'AppxManifest.xml'. Before the error I played a little bit with MainPage.xaml but I didn't save it. I tried deleting everything I added and return back to the state the project was throwing me this error but nothing. The error remains. And I have no clue what this error is + I can find nothing on internet. Any ideas?