Scrolling works only once

[bmcc81]

Hi,

I made a scrolling text box that I feed xml into.

The only thing is when I scroll down or up I can only get it to work once.

on (press) { 
_root.scrollingText_mc._y = - 10;
} 

I want it so that every time I that I press the button that I scrolls down.
Can anyone tell me where I've gone wrong.

Thanks,
Bmcc