Spoilers not working

Hi,
I’ve just installed this great plugin like I’ve done so many times before. But this time it isn’t working. Instead of displaying the dropdown (spoiler) it just shows the titel of the spoiler – like here http://sussannewexoe.dk.linux48.unoeuro-server.com/?page_id=198. The last sentence on the page is supposed to be a spoiler. Any idea what I might be doing wrong?
/Lene Maria

http://wordpress.org/extend/plugins/wp-ui/