Random image doesn't load?

Hi, I just applied the ‘load random background’ tutorial and it seems to work out fine. One problem though, the image always seems to be blank!???
it could be you have refresh or close your browser a few times before you see the blank image…
check out www.theworks.be
if you refresh your browser the second image should appear (or close your browser)

first image is blank???

How come?

Tx!