ImageButton image not rendered

I have a GridView control with PagerTemplate below it. In the PagerTemplate there are 4 ImageButtons for paging grid like previous/next. These ImageButtons have images assigned to them.
When I publish it on server or try it locally everything works fine. But when I publish the site on a laptop running IIS v5.1, images for the buttons are not rendered. This happens for both IE as well as Firefox. When I saw the rendered html, I found that src attribute is empty even though ImageUrl property is set. Below is the html
<asp:ImageButton CssClass="MidAlign" Text="First" CommandName="Page" CommandArgument="First" runat="server" ID="btnFirst" ImageUrl="~/Resources/Images/first.gif" TabIndex="50" />
Rendered html:
<input type="image" name="ctl00$cplLeftContent$grd_Pro ...