Using a custom webservice in a webpart

using System;
using System.Runtime.InteropServices;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Serialization;
using System.Security;
using System.Web.UI.WebControls;
using Microsoft.SharePoint;
using System.Collections.Specialized;
using Microsoft.SharePoint.WebControls;
using Microsoft.SharePoint.WebPartPages;
using System.Configuration;
using System.Data;
using System.Web.UI.HtmlControls;
[assembly: AllowPartiallyTrustedCallers]

namespace CustomWebServiceResult
{
    [Guid("bec42463-9e42-4ead-92ae-4723cf3f2c02")]
    public class CustomWebServiceResult : System.Web.UI.WebControls.WebParts.WebPart
    {
        GridView ServiceGridView;
        string strError = string.Empty;
        localhost.Service s = new localhost.Service();
        public CustomWebServiceResult()
        {
        }
        protected override void Render(HtmlTextWriter writer)
        {
            writer.Write(strError);
            try
            {
                ServiceGridView.RenderControl(writer);
            }
            catch (Exception ex)
            {
                writer.Write(ex.ToString());
            }
        }
        protected override void CreateChildControls()
        {

            try
            {
                ServiceGridView = new GridView();
                ServiceGridView.ID = "ServiceGridView";
                ServiceGridView.AutoGenerateColumns = false;

                BoundField bTitle = new BoundField();
                bTitle.HeaderText = "Task Name";
                bTitle.DataField = "Title";
                ServiceGridView.Columns.Add(bTitle);

                BoundField bStatus = new BoundField();
                bStatus.HeaderText = "Task Status";
                bStatus.DataField = "Status";
                ServiceGridView.Columns.Add(bStatus);

                BoundField bPriority = new BoundField();
                bPriority.HeaderText = "Task Priority";
                bPriority.DataField = "Priority";
                ServiceGridView.Columns.Add(bPriority);

                BoundField bStartDate = new BoundField();
                bStartDate.HeaderText = "Task Start Date";
                bStartDate.DataField = "StartDate";
                ServiceGridView.Columns.Add(bStartDate);
                s.UseDefaultCredentials = true;
                ServiceGridView.DataSource = s.getTasks();
                ServiceGridView.DataBind();
                this.Controls.Add(ServiceGridView);
            }
            catch (Exception ex)
            {
                strError += ex.ToString();
            }
        }
    }
}