GridView ile veri tabanından verileri çekiyorum çektiğim müşterilerin ismini alfabatik sıralayamıyorum

GridView in AutoSort özelliğini True yapıyorum sonra istediğim bölümün class ına SortExpression="KategoriAdi" tanımlıyorum çalıştırdığımda çalılşıyormuş gibi oluyor ama hiç bir işlem yapmıyor.

sebebi ne olabilir? ne yapmam lazım

kodlarım
aspx

<%@ Page Title="" Language="C#" MasterPageFile="~/Admin/adminmaster.master" AutoEventWireup="true" CodeFile="Musterilerilistele.aspx.cs" Inherits="Admin_Musterilerilistele" %>

<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
    <table border="1" cellpadding="0" cellspacing="0" width="100%">
        <tr>
            <th class="style6" height="41" scope="col" 
                style="color: #0066FF; text-align: left; background-color: #66CCFF">
                &nbsp;&nbsp; Müşteri Listesi</th>
        </tr>
        <tr>
            <td height="25">
                <table border="1" cellpadding="0" cellspacing="0" width="100%">
                    <tr>
                        <th class="style3" scope="col" width="20%">
                            Müşteri Adı Soyadı</th>
                        <th class="style3" scope="col" width="20%">
                            Kategorisi</th>
                        <th class="style3" scope="col" width="20%">
                            Firma Adı</th>
                        <th class="style3" scope="col" width="20%">
                            Cep Telefonu</th>
                        <th class="style3" scope="col" width="20%">
                            İlan</th>
                        <th class="style3" scope="col" width="20%">
                            Yer Göster</th>
                        <th class="style3" scope="col" width="20%">
                            <img border="0" src="Images/edit.png" /></th>
                        <th class="style3" scope="col" width="20%">
                            <img border="0" src="../images/sil.png" /></th>
                    </tr>
                </table>
            </td>
        </tr>
        <tr>
            <td>
                <asp:GridView ID="dlMusteriler" runat="server" AutoGenerateColumns="False" 
                    CellPadding="4" ForeColor="#333333" GridLines="None" 
                    onrowcommand="dlMusteriler_RowCommand" Width="100%" AllowSorting="True">
                    <AlternatingRowStyle BackColor="White" />
                    <Columns>
                         <asp:BoundField HeaderStyle-HorizontalAlign="Left" DataField="MusteriAdiSoyadi" HeaderText="MusteriAdiSoyadi" 
                            SortExpression="MusteriAdiSoyadi" >
<HeaderStyle HorizontalAlign="Left"></HeaderStyle>
                     
                        <asp:BoundField DataField="MusteriAdiSoyadi" HeaderText="Müşteri adı" />
                        <asp:BoundField DataField="FirmaAdi" HeaderText="Firma Adı" />
                        <asp:BoundField DataField="Cep" HeaderText="Cep Telefonu" />
                        <asp:BoundField DataField="MusteriAdminAD" HeaderText="Muşteri Sorumlusu" />
                        <asp:BoundField DataField="FirmaAdi" HeaderText="Firma Adı" />
                        <asp:HyperLinkField DataNavigateUrlFields="MusteriId" 
                            DataNavigateUrlFormatString="musteriiLanGoster.aspx?id={0}" 
                            DataTextField="HaberSayisi" HeaderText="H.Sayısı" />
                        <asp:HyperLinkField DataNavigateUrlFields="MusteriId" 
                            DataNavigateUrlFormatString="musteriHaberGoster.aspx?id={0}" 
                            DataTextField="yerGostermeSayisi" HeaderText="Yer.Sayısı" />
                        <asp:HyperLinkField DataNavigateUrlFields="MusteriId" 
                            DataNavigateUrlFormatString="MusteriGuncelle.aspx?id={0}" 
                            DataTextField="MusteriId" HeaderText="Düzenle" />
                        <asp:TemplateField HeaderText="Sil">
                            <ItemTemplate>
                                <asp:LinkButton ID="linkbuton" runat="server" 
                                    CommandArgument='<%#Eval("MusteriId") %>' Text="Sil"> </asp:LinkButton>
                            </ItemTemplate>
                        </asp:TemplateField>
                    </Columns>
                    <EditRowStyle BackColor="#7C6F57" />
                    <FooterStyle BackColor="#1C5E55" Font-Bold="True" ForeColor="White" />
                    <HeaderStyle BackColor="#1C5E55" Font-Bold="True" ForeColor="White" />
                    <PagerStyle BackColor="#666666" ForeColor="White" HorizontalAlign="Center" />
                    <RowStyle BackColor="#E3EAEB" />
                    <SelectedRowStyle BackColor="#C5BBAF" Font-Bold="True" ForeColor="#333333" />
                    <SortedAscendingCellStyle BackColor="#F8FAFA" />
                    <SortedAscendingHeaderStyle BackColor="#246B61" />
                    <SortedDescendingCellStyle BackColor="#D4DFE1" />
                    <SortedDescendingHeaderStyle BackColor="#15524A" />
                </asp:GridView>
          
            </td>
        </tr>
    </table>
</asp:Content>

aspx.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;

public partial class Admin_Musterilerilistele : System.Web.UI.Page
{

    public static string KategoriId = "";
    Fonksiyon system = new Fonksiyon();
    string islem = "";
    string MusteriId = "";
    protected void Page_Load(object sender, EventArgs e)
    {
        if (Session["AdminId"] == null)
        {
            Response.Redirect("Login.aspx");
        }

        KategoriId = Request.QueryString["KategoriId"];
        islem = Request.QueryString["islem"];
        MusteriId = Request.QueryString["MusteriId"];

        if (islem == "Sil")
        {
            system.cmd("Delete from Musteriler Where MusteriId=" + MusteriId);
            Response.Redirect("Musteriler.aspx");
        }

        DataTable dtMusteriler = system.GetDataTable("exec mustericek");
        dlMusteriler.DataSource = dtMusteriler;
        dlMusteriler.DataBind();


    }
    protected void dlMusteriler_RowCommand(object sender, GridViewCommandEventArgs e)
    {

        Response.Redirect("Musterilerilistele.aspx");
        system.cmd("Delete from Musteriler Where MusteriId=16");
        // Response.Redirect("Musteriler.aspx");

    }
  
}