Javascript scrollbar not working in hidden <DIV>s

[Sura]

Hi

I have a set of 3 DIVs. The first one is visible but the other two
gets visible on click. Each of them has a javascript scrollbar for
scrolling the content within. In the first DIV the scrolling works
fine, yet in the 2nd or 3rd DIV the scrolling dont work.
See this link: http://application.timeus.net/pressreleases/scroll/food2.html

Whereas if I keep all the DIVs visible, then scrolling in all of them
works.
See this link: http://application.timeus.net/pressreleases/scroll/food.html

Can anybody put some light on why the srcolling is not working in the
hidden DIVs.

Thanks
Sura