Scroll bar

Well written plugin.

I would like to know if there is any way I can add a scroll bar to the pop-up?
I have changed this in the css:

#displetpop .popupinner {
overflow: scroll;
padding-bottom: 27px;
}

The pop-up now displays a scrollbar but I am unable to scroll.

http://wordpress.org/extend/plugins/displet-pop/