List box pops back to the first item after SelectedIndexChange event fires.

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C#

ASP.NET

I have a 3 dropdownlist control with a selectedindexchanged event that fires correctly. However, when you select an item from the list the index value that is returned to the selectedindexchanged event does not change; the list box pops back to the first item in the list. Any help would be appreciated. ~Dharmendra~

public partial class Production : System.Web.UI.Page
    { 
        EmployeeQuotientCL.Production _production = null;
        DataSet dsNatureOfWork = new DataSet();
        DataSet dsProjectRegion = new DataSet();
        DataSet dsCountyDetails = new DataSet();
        DataSet dsWorkType = new DataSet();
        DataSet dsTask = new DataSet();
       

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                 string userEcode=Convert.ToString(Session["UserID"]); 
                _production = new EmployeeQuotientCL.Production();                       
                dsNatureOfWork = _production.GetNatureOfWork();
                if (dsNatureOfWork.Tables[0].Rows.Count > 0)
                {
                    BindDdlNatureOfWork(dsNatureOfWork);
                }
                else
                {
                }
            }            

        }


        
        public void BindDdlNatureOfWork(DataSet dsNatureOfWork)
        {
            ddlNatureofWork.DataSource = dsNatureOfWork.Tables[0];
            ddlNatureofWork.DataTextField = "NatureOfWorkName";
            ddlNatureofWork.DataValueField = "NatureOfWorkID";
            ddlNatureofWork.DataBind();
            ddlNatureofWork.Items.Insert(0, "--Select Nature of Work--");
        }

        public void FillRegionProject(int NatureOfWorkID)
        {
            if ((NatureOfWorkID != null) || (NatureOfWorkID != 0))
            {
                _production = new EmployeeQuotientCL.Production();
                dsProjectRegion = _production.GetProjectRegion(NatureOfWorkID);
                if (dsProjectRegion.Tables[0].Rows.Count > 0)
                {
                    ddlRegionProjectName.DataSource = dsProjectRegion.Tables[0];
                    ddlRegionProjectName.DataTextField = "RegionProjectName";
                    ddlRegionProjectName.DataValueField = "RegionProjectID";
                    ddlRegionProjectName.DataBind();
                    ddlRegionProjectName.Items.Insert(0, "--Select Region/Project--");

                }
                else
                {
                }
            }

        }

        protected void ddlRegionProjectName_SelectedIndexChanged(object sender, EventArgs e)
        {
            int RegionProjectID = Convert.ToInt32(ddlRegionProjectName.SelectedValue.ToString());
            FillCounty(RegionProjectID);
            ddlRegionProjectName.SelectedIndex = 0;
        
        }

        public void FillCounty(int regionprojectID)
        {
            if ((regionprojectID != null) || (regionprojectID != 0))
            {
                _production = new EmployeeQuotientCL.Production();
                dsCountyDetails = _production.GetCounty(regionprojectID);
                if (dsCountyDetails.Tables[0].Rows.Count > 0)
                {
                    ddlCountyName.DataSource = dsCountyDetails.Tables[0];
                    ddlCountyName.DataTextField = "CountyName";
                    ddlCountyName.DataValueField = "CountyID";
                    ddlCountyName.DataBind();
                    ddlCountyName.Items.Insert(0, "--Select County--");

                }
                else
                {
                }
            }
        }

        protected void ddlNatureofWork_SelectedIndexChanged(object sender, EventArgs e)
        {
            int NowID = Convert.ToInt32(ddlNatureofWork.SelectedValue.ToString());
            FillRegionProject(NowID);
            ddlRegionProjectName.SelectedIndex = 0;
        }
   
    }
}