Mask a runtime created gradient fill

programming flash
1

I m having problems in masking a gradient fill created at runtime. Actually i had a movieClip an then at runtime created three movieClips
1.gradient filled rectangle mcGrad,
2.loader to load an image mcLoader
3.a curved rectangle mcMask

trying to mask mcGrad and mcLoader with mcMask
image gets masked but mcGrad not, i m writing as-:

mcGrad.setMask(mcMask);
mcLoader .setMask(mcMask);