Error message "Can't Add Script"

I keep getting the error message "Can't Add Script Can;t add component "NewBehaviourScript" b/c it doesn't exist. Check to see if the file name and class name match". I'm on version 4.6.1f1 of Unity, on a mac running OS 10.8.3 I can no longer add new or old scripts which I had successfully added to the game objects previously. If I open another Unity project, I am able to add scripts to game objects with no error messages. If I create a 'clean' script like "NewBehaviourScript" , I cannot add it to the sphere object. Is it possible that my project is corrupt?