Simple AS problem!?

I am getting crazy with this problem…
Simply, I want to display a pink colored square inside the gray area when I press the button I
have on my scene but It wont work. When I debugg the movie there is a problem at row #10.

Please download my FLA file here: http://www.mediafire.com/?djadmrxmmmb
Help me with this simple(?) problem!

Thx in advance!