How to mask a Symbol

Hi,

Can anyone help me on this…

I have a symbol in my stage. He is masked by a circle.

I want that when I click on the Symbols, the mask expands  and reveals what is behind it. Like this :

I followed the threat “I want to know how masking objects or image.“ where redesign gave a sample with a mask.

When I try to do the same thing,  is like the mask is always at position 0 0 and not over my symbol that is placed in the stage at position 795 570. Giving a mask-position doesn’t change anything. My symbol is invisible.

Hope I make myself clear ...

Thanks a lot for any hints.

s.