Could you try below -
protected void Application_Start(object sender, EventArgs e)
{
RegisterRoutes(RouteTable.Routes);
}
public void RegisterRoutes(RouteCollection routes)
{
routes.MapPageRoute("IC", "IC", "~/Page1.aspx");
}
Have your link as -
<asp:LinkButton ID="lnkLC" runat="server" OnClick="lnkLC_Click">IC_PAGE_TEST</asp:LinkButton>
and then have your event as -
protected void lnkLC_Click(object sender, EventArgs e)
{
Response.RedirectToRoute("IC");
}