Help me with GridView Control

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C#

ASP.NET

.NET

Hello, i have a problem with GridView Paging.
Here is my code:

<asp:GridView ID="grdGroupAsManager" runat="server" AutoGenerateColumns="false" ShowHeader="true" EmptyDataText="Empty" 
	 RowStyle-HorizontalAlign="Left" 
    AllowPaging ="true" PageSize="10" DataKeyNames="RelatedItemTitle" Width="800px" OnPageIndexChanging="grdGroupAsManager_SelectedIndexChanging">
    <Columns>
here is templates
</Columns>
</asp:GridView>

protected void grdGroupAsManager_SelectedIndexChanging(object sender, GridViewPageEventArgs e)
       {
           GridView gvTasksAsManager = (sender as GridView);
           gvTasksAsManager.PageIndex = e.NewPageIndex;
           InitTasksForMeAsManager(gvTasksAsManager);
       }
       protected void InitTasksForMeAsManager(GridView grdGroupAsManager)
       {
           SPSite site = SPContext.Current.Site;
           SPWeb edms = SPContext.Current.Web;
           SPUser user = SPContext.Current.Web.CurrentUser;
           SPListItem employee = GetSPUserEmployee(SPContext.Current, user);
           string employeeID = (employee != null) ? employee.ID.ToString() : "0";
           SPList negotiationTasks = edms.GetList(SPUrlUtility.CombineUrl(edms.Url, "Lists/ContractNegotiationTasks"));
           SPListItemCollection tasks = GetNonCompletedUserTasks(negotiationTasks, "Manager", employeeID.ToString());
           DataTable firstresult = ProcessTasksLinks(tasks, edms, negotiationTasks);
           DataTable ex = firstresult.Copy();
           DataTable result = RemoveDuplicateRows(ex, "RelatedItemTitle");
           ViewState["TasksAsManager"] = firstresult;
           grdGroupAsManager.DataSource = result;
           grdGroupAsManager.DataBind();
       }
protected void Page_Load(object sender, EventArgs e)
       {
           try
           {
               if (!Page.IsPostBack)
               {
                   grdGroupTasks.PagerTemplate = grdGroupAsManager.PagerTemplate = null;
                   InitTasksForMeAsManager(grdGroupAsManager);
                   BindGroupTasks(grdGroupTasks);
               }
           }
           catch (Exception ex)
           {
               SPDiagnosticsService.Local.WriteTrace(0, new SPDiagnosticsCategory(
                   "55EDMS", TraceSeverity.Unexpected, EventSeverity.Error), TraceSeverity.Unexpected, ex.Message, ex.StackTrace);
           }
       }

When i click to next page index, for example was first page, and i click to second page.
Gridview proceeds to second page, but i cannot see row with Page Indexes..
When i delete if (!Page.IsPostBack) from Page_Load, all Works Fine, but i don't need bind gridview on every postBack, what i do wrong?HELP PLEASE