AS3 Button Scripts in document class

I’m suffering through my first AS3 site. It’s not very complicated, but I cannot get my buttons to work.

Here is my new document class.
http://talesfromthehead.com/random/doc_class4.txt

And here are the errors I got for each mention of b1_mc, which is just a movie clip on the stage.

1120: Access of undefined property b1_mc

Since I have import flash.display.MovieClip; at the top of my class, why do I keep getting this error?