EDIT
After looking at your .fla, I can see your issue:
On your first frame, you have the following script:
stop();
addEventListener(MouseEvent.CLICK, StartGame);
function StartGame(event: MouseEvent): void
{
nextFrame();
}
You likely aren't aware that the mouse click listener you add there, doesn't go away until you tell it to (even if the frame changes). That's why every click calls next frame.
To remedy this, simply remove the listening before you move on to the next frame:
function StartGame(event: MouseEvent): void
{
removeEventListener(MouseEvent.CLICK, StartGame);
nextFrame();
}