From my previous post on background-size attribute on CSS, the said code doesn't seem to work on lower version of IE specifically IE8. From experience on web designing, dealing with different Internet Explorer versions is really a pain.
Anyway, to solve this issue, here is a simple additional CSS attribute that you can use to resolve it.
filter: progid:DXImageTransform.Microsoft.AlphaImageLoader( src='[IMAGE HERE]', sizingMethod='scale'); -ms-filter: "progid:DXImageTransform.Microsoft.AlphaImageLoader( src='[IMAGE HERE]', sizingMethod='scale')";
With the code above, simply replace the
[IMAGE HERE]with the correct location of your image to use.
Unfortunately, the code above scales the image to fit the entire area that it covers. So if you are using a sprite to cover as your background, this might bring more issues.