ajax返回空值

<script language="javascript" type="text/javascript">

function statusResult()
{
var ss=document.getElementById("ddlStatus");
AjaxMethod.GetStatusWhyList(ss.value,get_status_Result_CallBack);
}

function get_status_Result_CallBack(response)
{
if (response.value != null)
{
document.all("ddlStatusWhy").length=0;
var ds1 = response.value;
if(ds1 != null && typeof(ds1) == "object" && ds1.Tables != null)
{
for(var ii=0; ii<ds1.Tables[0].Rows.length; ii++)
{
var name1=ds1.Tables[0].Rows[ii].Title;
//alert(ds1.Tables[0].Rows.length);
var id1=ds1.Tables[0].Rows[ii].Title;
document.all("ddlStatusWhy").options.add(new Option(name1,id1));
}
}
}
return
}
</script>

ds1.tables[0].rows[ii].title返回undefault
ds1.Tables[0].Rows.length返回的数字正常
请各位大侠帮忙看一下,谢谢

ajaxMethod.cs:
#region GetDataSet
public static DataSet GetDataSet(string sql)
{
string SqlConnString = System.Configuration.ConfigurationManager.ConnectionStrings["connstr"].ConnectionString;
SqlDataAdapter sda = new SqlDataAdapter(sql, SqlConnString);
DataSet ds = new DataSet();
sda.Fill(ds);
return ds;
}
#endregion

#region GetStatusList
public static DataSet GetStatusList()
{
return GetDataSet("select id,title from ConsultBigType order by id desc");
}
#endregion

#region GetStatusWhyList
[Ajax.AjaxMethod(Ajax.HttpSessionStateRequirement.Read)]
public DataSet GetStatusWhyList(string ss)
{
string sql = "select id,BigType,title from ConsultSmallType where BigType='" + ss + "'";
return GetDataSet(sql);
}
#endregion