Link to the page? Most likely, there is some element inside the shell that breaks through the browser window.
Often this happens with padding and width. Keep in mind if you have an element inside the wrapper that is set to 100% width and you add padding to the left and right of 20 pixels. It will create a horizontal scrollbar because the item is 100% + 40 px.
So, if you are building fluid elements inside a div, you would do it like this:
#liquidelement { width:96%; padding:0 2%; }
You need to subtract the indentation from the width, and also always use percentages for laying when performing layouts, because they are fluid and not fixed.
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