Question about Pom's Tutorial: Drawing Board

this question is in reference to this thread: http://www.kirupa.com/developer/actionscript/drawingboard.htm

I am having some difficulty turning thr lines that are drawn into a mask. . .

I am using set mask in this way, with the code provided in the tutorial:

test_mc.setMask(line);

Where the line mc is the mask and test_mc is being masked.

I have tried placing it within the onEnterFrame and onMouseDown function with no success

Thanks in advance . . .