This usually happens with Desktop PCs / laptops with older version of the DirectX driver or video card. The problem itself is related to the DirectX CSS filters under IE - we use them in order to achieve a transparent modal overlay in IE. The other browsers do not use that Activex component, as they have utilized pure css opacity, and respectively the problem does not occur.
In this case I recommend you reduce the page size in order to make the page works properly. Also, you can use a non-modal RadWindow
control and avoid using any animation on the page. All of the transparency animations use the same DirectX filters under IE and may cause the same problem.
Kashif, regarding your second question - how do you open the RadWindow?
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