C# - GridView PageIndexChanging Not Working

This seems to be an easy question to ask, but I am not able to show items in GridView. Here is my code:

public partial class TestList : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{ TestProject.DataAccess.Repository.Instance.Initialize(Settings.Default.TestConnection);
BindData();
}
}
private void BindData()
{
//Restriction Info!!
gvAgentList.DataSource = EntityRegistration.DataAccess.Repository.Instance.GetData();
gvAgentList.DataBind();
}
protected void gvAgentList_PageIndexChanging (object sender, GridViewPageEventArgs e)
{
gvAgentList.PageIndex = e.NewPageIndex;
gvAgentList.DataBind();
}
private string ConvertSortDirectionToSql(SortDirection sortDirection)
{
string newSortDirection = String.Empty;
switch (sortDirection)
{
case SortDirection.Ascending:
newSortDirection = "ASC";
break;
case SortDirection.Descending:
newSortDirection = "DESC";
break;
}
return newSortDirection;
}
protected void gvAgentList_Sorting(object sender, GridViewSortEventArgs e)
{
DataTable dataTable = gvAgentList.DataSource as DataTable;
if (dataTable != null)
{
DataView dataView = new DataView(dataTable);
dataView.Sort = e.SortExpression + " " + ConvertSortDirectionToSql(e.SortDirection);
gvAgentList.DataSource = dataView;
gvAgentList.DataBind();
}
}
}
Here is the markup of the GridView:
<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
<p>
Agent Lists:</p>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:GridView runat ="server" ID = "gvAgentList"
AllowPaging = "True"
AutoGenerateSelectButton="True" AllowSorting="True" BackColor="#E8E8E8"
BorderColor="#003399" BorderStyle="Solid" BorderWidth="1px" Height="375px"
Width="731px" OnPageIndexChanging = "gvAgentList_PageIndexChanging"
OnSorting="gvAgentList_Sorting" >
<AlternatingRowStyle ForeColor="#0066CC" />
<HeaderStyle ForeColor="#3366FF" />
</asp:GridView>
<asp:SqlDataSource ID="SqlDataSource1" runat="server"></asp:SqlDataSource>
</ContentTemplate>
</asp:UpdatePanel>
</asp:Content>

The problem is that my GridView is not throwing me any exception and through breakpoints I can see that the function is called in code behind.