Hello,
Here is a link to the background image:
http://shape5.com/demo/seaofglass/images/stories/clouds.jpgIf you are working with Joomla 1.5 and used the SQL or site shaper open up the menu item that you default background isn't showing on and then resave it. Most likely it is looking for an old background used in Joomla 1.0.x and kept this settings durring the upgrade to Joomla 1.5.
Or you can post a URL and I'll take a look at it.
Regards,