Weird weird mask problem

For some reason, all of a sudden, I’m experiencing a weird problem:

If I load an external swf into a movie clip that has a mask, the swf fails to show up. Delete the mask, and the swf appears. Put the mask back in, and POW! no swf.

The odd thing is, a project I authored a few weeks ago, with masks, works just fine!

Anybody else experience this issue??

I’m running OSX Tiger on a G5 dual processor.