1017: The definition of base class MovieClip was not found

programming flash
1

As the title says, that is the error I am getting. It pinpoints this error at line 2 of the following code for my very basic class:

package  {    
    import flash.display.MovieClip;
    public class Block extends MovieClip{
        public function Block() {
            // constructor code
        }
    }
}

If you need more info, lemme know.