Cascading drop down issue

I wrote a webservice for cascading dropdownlist as given below

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Text;
using System.Data;
using System.Web.Script.Services;
using AjaxControlToolkit;
using System.Collections.Specialized;

/// <summary>
/// Summary description for WebService2
/// </summary>
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line.
[System.Web.Script.Services.ScriptService]
public class WebService2 : System.Web.Services.WebService {

    public WebService2()
    {

        //Uncomment the following line if using designed components
        //InitializeComponent();
    }

    [WebMethod]
    public string HelloWorld() {
        return "Hello World";
    }



    [ScriptMethod()]
    [WebMethod]
    public AjaxControlToolkit.CascadingDropDownNameValue[] GetDropDownContentsfrom(string knownCategoryValues, string category)
    {

        StringDictionary kv = CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues);

        string[] str = knownCategoryValues.Split(':', ';');

        if (str.Length < 1)
        {
            return null;
        }

        string _ProjectIDs = str[1].ToString();



        DataSet _Ds = new DataSet();
        DBTask objDBTask = new DBTask();

        StringBuilder objBuilder = new StringBuilder();




        objBuilder.Append(" SELECT dbo.RntProjectLocationSettings.LocationID, ");
        objBuilder.Append(" dbo.RntLocation.Location ");
        objBuilder.Append(" FROM dbo.RntProjectLocationSettings INNER JOIN ");
        objBuilder.Append(" dbo.RntLocation ON ");
        objBuilder.Append(" dbo.RntProjectLocationSettings.LocationID = dbo.RntLocation.LocationID ");
        objBuilder.Append(" WHERE dbo.RntProjectLocationSettings.ProjectID=  " + _ProjectIDs.ToString());   //NOT WORKING

        //objBuilder.Append(" WHERE dbo.RntProjectLocationSettings.ProjectID= 2 " );   ITS WORKING  FINE




        _Ds = objDBTask.ExecuteDataset(objBuilder.ToString());


        List<AjaxControlToolkit.CascadingDropDownNameValue> cascadingValues = new List<AjaxControlToolkit.CascadingDropDownNameValue>();

        foreach (DataRow dRow in _Ds.Tables[0].Rows)
        {
            string _LocationID = Convert.ToString(dRow["LocationID"].ToString());
            string _Location = Convert.ToString(dRow["Location"].ToString());
            cascadingValues.Add(new AjaxControlToolkit.CascadingDropDownNameValue(_Location, _LocationID));
        }

        return cascadingValues.ToArray();
    }



    
}

The line
objBuilder.Append(" WHERE dbo.RntProjectLocationSettings.ProjectID= 2 " ); is working but the line
objBuilder.Append(" WHERE dbo.RntProjectLocationSettings.ProjectID= " + _ProjectIDs.ToString()); is not loading the dropdown list.
Can any one point out the error .


The source code in designer is

<cc1:CascadingDropDown ID="CascadingDropDown4" runat="server" Category="_ProjectIDs"
ParentControlID="ddlProject" ServiceMethod="GetDropDownContentsfrom"
TargetControlID="ddlLocation" ServicePath="WebService2.asmx">
</cc1:CascadingDropDown>


Thanks in advance to all..