Button under a mask

Hey,
I'm pretty new to flash, and i'm having a bit of a problem with a navigation im putting together. I have created a simple button, which when rolled over reveals a bar with sub navigation buttons. The problem i'm having is when i rollover the first button, and the bar reveals itself, the sub navigation buttons are unresponsive. I have a feeling that this maybe down to the mask used in the layer about it. The other problem i seem to be having is sectioning off the area that I want clickable, because at the moment when i hover the mouse over the area outside of the actual button, the animation is triggered.

Sorry if the explanation of the problem was a bit confusing. I have also provided the .fla file that I have been working on.

Thanks
gb207