Mask within a mask? Not Working for me

Hello, I am trying to create a gradient mask within a masked clip. Is this possible? Everytime i try to add the outer mask, they stop working.

here is my gradient mask code:

[AS]
mNav.bHold.cacheAsBitmap=true
mNav.mask.cacheAsBitmap=true
mNav.bHold.setMask(mNav.mask);
[/AS]
but when i try to add the outer mask… it s stops working:
[AS]
mNav.setMask(mMask)
[/AS]

any insight?
Thanks,
Q