Why is this error happening ?

Hi, I have created a project where I am testing some services for my game and everything was working fine until today. When i play the game in editor this error appears in console: "DirectoryNotFoundException: Directory '/Applications/Unity/Unity 2017.1.2f1.app/PlaybackEngines/AndroidPlayer' not found. System.IO.Directory.GetFileSystemEntries (System.String path, System.String searchPattern, FileAttributes mask, FileAttributes attrs) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.IO/Directory.cs:514)" Why is this error happening ? Has anyone encountered the same error before ? Thank you, Gerald.