System.Web.HttpException: Response is not available in this context.

I want to redirect user to SessionExpPage.aspx page on session timeout. To achieve this I added following code to one of the method of Global.asxs file of my application. But I am getting this error messge : "System.Web.HttpException: Response is not available in this context"
void Session_End(object sender, EventArgs e)
{ try { Response.Redirect("~/SessionEx ...