Hi Irene,
I belive the problem is with the image footer5.gif
Do not touch the css, just replace your footer5.gif with this one from zip file

It works now on my computer

--------- Update:
By the way, the picture footer5.gif has white space which width is 2 px on the right side (whch is visible when you zoom in), and pictures width is total 818px. This may happen when you sliced the design.. It would be the best to remove 2px white space and make it 816 as it is bg.gif.
Also, I suggest to add width: 816px in the #footer-valid
I hope I helped..
cheers