if (Sessions.Current.authenticated != null)
    {
        if (Sessions.Current.authenticated)
        {
            Response.Redirect("Admin/Default2.aspx");
        }
    }
}

protected void login(object sender, EventArgs e)
{
    string username = txtUsername.Text.ToString();
    string password = txtPassword.Text.ToString();

    DataTable dtUser = DBConnector.getTable("SELECT * FROM User WHERE Username = '" + username + "' AND Password = '" + password, false);
    if (dtUser.Rows.Count > 0)
    {

        DataRow dr = dtUser.Rows[0];
        Sessions.Current.authenticated = true;
        Sessions.Current.lastfirst = dr["Name"].ToString();
        Sessions.Current.Usertype = dr["userType"].ToString();


        Response.Redirect("Admin/Default2.aspx");
        Response.Redirect("web/Default.aspx");
    }
}