The following setup will cause an Invalid Argument error in IE8:

			<div style="display: none;">
					<telerik:RadFileExplorer runat="server" ID="RadFileExplorer1"
											 Width="700px" Height="520px" RenderMode="Lightweight">
											 <Configuration ViewPaths="~/images" />
					</telerik:RadFileExplorer>
			</div>

It can extend to a FileExplorer in a MultiPage, for example.

Solution for the time being is to avoid using RenderMode=Lightweight for IE8