“Packages cannot be nested” error in Flex

I want to use SoundFacade class from Adobe. (Here, from github). I simple created an "ActionScript File" and paste all the code. But when I want to compile my app I got following error:

1037: Packages cannot be nested.

The only reason I can guess is that the package must somehow put into the project or something.

Even when I just put a simple empty package I got the error:

package{  }

Any idea what is this error about?