Random Motion with Mask?

Is it possible to do? What I would like to do is add random motion to a circle and then mask it. When I do so it ceases to move but when I turn masking off it stops. Is there any way to make it work. I am using the random motion that I found here on Kirupa at: http://www.kirupa.com/developer/actionscript/random.htm
Thanks in advance,
Duke

I have my source file attached as well.