Hello there are two ways to do this according to you stylesheet

first which is the better way probably
stylesheet.css (line 208)
#contentMainWrapper {
background-color:#FFFFFF;
margin:0px 0em 0em;
}
second
stylesheet.css (line 208)
#contentMainWrapper {
background-image:url(../images/centerbox.jpg);
background-repeat:repeat;
margin:0px 0em 0em;
}
In the second method I repeated your background image which fixes it but it really doesnt make sense because you background image is a 200 x 200 white square. So if you do away with it and use the background-color, it will speed up on your loading time and query slightly.