Issue with masking/layer order

Hi everyone! I followed the random animated bubble effect tutorial found here: http://the-dude.co.uk/tutorials/flash-tutorial-on-creating-random-anim ated-bubbles-as2/ and the effect itself is exactly what I need. However, the bubbles show up on top of everything else in my animation (other graphics, text, etc.), and I need them to appear in the background only. Even if I change the layer order or create a mask, the bubbles STILL show up on top of everything. Any suggestions on how to fix this?