Quote - you have a new runtime folder added somewhere inside the runtime folder (I''ve had that happen quite often). If that is the case drag it up to content and drop it back in. It will tell you there is already a runtime folder and that's fine just go ahead and let it put it in there.

Not on the Mac. There, if you drop one Runtime folder on top of another it will replace the existing folder with the one you move. Instead you have to move the files (or folders if they aren't already there) from the RuntimeRuntime folder to the equivalent location in the proper Runtime folder.