这样一条SQL语句咋会出错哩？？？耽误大家几分钟时间帮忙看下！！谢了！！！

        Session["fbsj"] = txtfbsj.Text;

        Session["zldw"] = txtzldw.Text;

        Session["zlr"] = txtzlr.Text;

        Session["zlzt"] = ddlzlzt.SelectedValue;

        Session["bt"] = txtbt.Text;

        Session["fkqx"] = txtfkqx.Text;

        Response.Redirect("YanPanSelectResult.aspx");

        SqlConnection con = SqlCon.GetSqlConnection();

        SqlDataAdapter da = new SqlDataAdapter("select * from jh_zlxx where ((@fbsj is null or zlxx_fbsj=@fbsj) and   (@zldw is null or zlxx_zldw=@zldw) and  (@zlr is null or zlxx_zlr=@zlr) and (@zlzt is null or zlxx_zlzt=@zlzt))",con);

        da.SelectCommand.Parameters.AddWithValue("@fbsj", Session["fbsj"]);

        da.SelectCommand.Parameters.AddWithValue("@zldw",Session["zldw"]);

        da.SelectCommand.Parameters.AddWithValue("@zlr",Session["zlr"]);

        da.SelectCommand.Parameters.AddWithValue("@zlzt",Session["zlzt"]);

        DataSet ds = new DataSet();

        da.Fill(ds, "SelectResult");



        gdvFaBu.DataSource = ds;

        gdvFaBu.DataBind();