setMask problem with Multiple Movieclips

trying to use the setMask method and having trouble.

I have it working on my dynamic text, but I am trying to mask the movieclip that is loading my image from the server.

I have a moviclip called Comments.

and in it I have movieclips called textbox and image

I have one setMask AS like this for the textbox
this.textbox.setMask(this.mc_mask2); - this one works

But for image I have the same thing and it doesnt work. I have
this.image.setMask(this.mc_mask);

Can anyone help me understand why it doesnt work.