System.Web.Security.FormsAuthentication.SetAuthCookie(tbUSERNAME.Text, false);
Response.Redirect("~/Admin/Default.aspx");

private string AuthenticatedUser = "";

        protected void Page_Init(object sender, EventArgs e)
        {
            try
            {
                string temp = this.Page.User.Identity.Name;
                AuthenticatedUser = temp;
            }
            catch
            {

            }
            if (String.IsNullOrEmpty(AuthenticatedUser) == false)
            {
                //normal Page_Init code
            }
        }

/// <summary>
/// Registers a Script with the Client-Side code to keep a user Session alive
/// </summary>
/// <remarks>
/// Adapted from: http://www.codeproject.com/KB/session/Reconnect.aspx
/// </remarks>
private void RegisterSessionKeepAlive()
{
	try {
		// NOTE: Everything needs converted to milliseconds
		int timeoutWindow = 30;		// Number of seconds before session will timeout to fire a simulated PostBack to renew Session
		int timeout = (this.Session.Timeout * 60000) - (timeoutWindow * 1000);
		// if (System.Diagnostics.Debugger.IsAttached) timeout = 10000;	// For Testing, comment if not needed
		string reconnectUrl = VirtualPathUtility.ToAbsolute("~/Common/SessionReconnect.aspx");
		string startupScript = string.Format("window.setInterval('reconnectSession()', {0});\n", timeout); //Set to length required
		string scriptKey = "SessionReconnectScript";
		string startupScriptKey = "SessionReconnectStartupScript";

		ScriptManager sm = ScriptManager.GetCurrent(this.Page);
		if (sm != null && sm.IsInAsyncPostBack)
			ScriptManager.RegisterStartupScript(this.Page, this.Page.GetType(), startupScriptKey, startupScript, true);
		else {
			if (!Page.ClientScript.IsClientScriptBlockRegistered(this.Page.GetType(), scriptKey)) {
				System.Text.StringBuilder script = new System.Text.StringBuilder();
				script.Append("var reconnectCount = 0;\n");	// Number of Reconnects
				script.Append("var reconnectMax = 5;\n");	// Maximum Reconnects
				script.Append("function reconnectSession(){\n");
				script.Append("\treconnectCount++;\n");
				script.Append("\tif (reconnectCount < reconnectMax){\n");
				script.Append("\t\twindow.status = 'Session Refreshed ' + reconnectCount.toString() + ' time(s)';\n");
				script.Append("\t\tvar img = new Image(1,1);\n");
				script.AppendFormat("\t\timg.src = '{0}';\n", reconnectUrl);
				script.Append("\t}\n");
				script.Append("}\n");
				Page.ClientScript.RegisterClientScriptBlock(this.Page.GetType(), scriptKey, script.ToString(), true);
			}

			if (!Page.ClientScript.IsStartupScriptRegistered(this.Page.GetType(), startupScriptKey))
				Page.ClientScript.RegisterStartupScript(this.Page.GetType(), startupScriptKey, startupScript, true);
		}

	}
	catch (Exception) { throw; }
}