Do you have in your project two scripts (js, cs or boo) called the same but written in two different languages? I had this case and for me it was having FogOfWar.cs and FogOfWar.js files.
For those of you trying to find duplicate scripts with the same name, in the project view, click the icon with the shapes (search by type) and select Scripts. All your scripts will be in the window in alphabetical order, just look for dupe C# and js ones.