I think this is due to the problem of CSS in diffrent version. I think if you use diffrent css file for different IE it will ok. For example, if IE less than or equal to version 7 then the upper portions css will work. If IE is greater than 6 than then the lower portion of css will work.

 <!--[if lt IE 7]>
    <link rel="Stylesheet" href="Styles/StyleSheet.css" type="text/css" />
    <link rel="Stylesheet" href="Styles/common.css" type="text/css" />
    <![endif]-->
    <!--[if gt IE 6]>
    <link rel="Stylesheet" href="Styles/StyleSheet_IE7.css" type="text/css" />
    <![endif]-->

You can try in this way. Hopefully, this will work.

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