Audio off & on

I have a lingering question that I cannot seem to get past.
I have a project which I have to do that needs to have a sound Off/On button.
I assume that in order to do this you have got to build an interface frame with the off/on button. Then I am loading my .swf into the interface by targeting a blank MC.
It works fine with the first swf that I load I can shut off or turn on the sound with no problem.
The problem begins when I unload the first movie then load the second movie in the same place. the sound button no longer works.

Any ideas or help someone might offer would be greatly appreciated.

Thanks,
Janet