Hello Marc,
I recently have seen a similar problem and a resolution to the problem in this forum thread - please, take a look and let us know if this helps.
http://forums.infragistics.com/forums/t/11424.aspx
I would guess that the ./ syntax is not mapped correctly in browsers,
<Image Url="./styling/Default/images/button_officeBlue.gif" />
You can try using ~/ instead of ./ and see how it goes.