Apply your effects first. Now choose your layer and under "Layer" choose precompose "shift+cntl+c"(PC), now you can apply your mask.
Another method would be to create a layer(solid) over your effected layer, add a mask to that layer and change your effected layers Track Matte to alpha.
Johnny Cuevas, Editor
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.