Problem with custom images using a TreeView

[LetsGoPens]

Hello,

I have a TreeView that I am modifying for accessibility purposes. Everything must be enlarged for use on a touch screen. I was able to enlarge the font and padding for the nodes without a problem. Now I need to enlarge the Expand/Collapse images for the nodes. I manually edited some .gif images to expand them. I can't get the TreeView to use the specified images though.

<asp:TreeView ID="TreeView1" ExpandDepth="0" PopulateNodesFromClient="true" BackColor="OldLace" BorderColor="Black" BorderStyle="Solid"
     ShowLines="true" ShowExpandCollapse="true" OnSelectedNodeChanged="TreeView1_Select" PathSeparator="|"
     runat="server" NodeStyle-NodeSpacing="5" NodeStyle-Font-Size="24" NodeStyle-HorizontalPadding="10" EnableClientScript="False" 
     ImageSet="Custom" CollapseImageUrl="minus_r.gif" ExpandImageUrl="plusik_r.gif" >
     <NodeStyle Font-Size="24pt" HorizontalPadding="10px" NodeSpacing="5px" />
</asp:TreeView>

Any ideas as to why my images are not being picked up?

Thanks