The type or namespace name `Unity' does not exist in the namespace `UnityEditor.Facebook'

I'm developing a moblie app, and I get this error: The type or namespace name "Unity" does not exist in the namespace "UnityEditor.Facebook" ![alt text][1] ![alt text][2] What can I do to fix this? [1]: http://image.prntscr.com/image/412677f138274b0aaab435d4964e686f.png [2]: http://image.prntscr.com/image/4768393bfa18473fae880f4c812d2fd6.png