The name 'txtPWD' does not exist in the current context pls sove error

con.Open();
        SqlCommand cmd = new SqlCommand("select * from UserInformation where UserName =@username and Password=@password", con);
        cmd.Parameters.AddWithValue("@username",txtUserName.Text);
        cmd.Parameters.AddWithValue("@password",txtPWD.Text);
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataTable dt = new DataTable();
        da.Fill(dt);
        if (dt.Rows.Count > 0)
        {
            Response.Redirect("Details.aspx");
        }
        else
        {
            ClientScript.RegisterStartupScript(Page.GetType(), "validation", "<script language='javascript'>alert('Invalid Username and Password')</script>");
        }
    }