On the photo gallery page there is a rule coming from a ihover.css file, That sets the background-repeat to repeat-x only
background: url(../images/bg_header.jpg) repeat-x
The background you set on the header is inheriting that property and therefore is not being repeated in Y like on the other pages
Solution is to add a background-repeat property on the header background to force the repeat on both direction
On a side note, I am not sure why you are using a header image for what looks like a flat color. Why dont you set the header background color instead?