gridview Paging not selecting current page

I have select all checkbox for checking/unchecking gridview as shown below: when grid has one page only,everything workings fine, when there are multiple pages my JavaScript throws me an error "JavaScript runtime error: Unable to get property 'checked' of undefined or null reference".

Please find the javascript code

 function HeaderClick(CheckBox)
                {
                var MainGridView =document.getElementById("GriduwgDocuments");
                 if (CheckBox.checked == true)
                {
                for( var i=1; i < MainGridView.rows.length; i++)
               {
                 debugger;
               var chb = MainGridView.rows[i].cells[0].childNodes['1'].checked;
                    if (!chb.checked) {
              MainGridView.rows[i].cells[0].childNodes['1'].checked = true;
                                }
               }
               CheckBox.checked == true;
               }

               if (CheckBox.checked== false)
                {

                 for( var i=1; i < MainGridView.rows.length; i++)
               {
               var chb = MainGridView.rows[i].cells[0].childNodes['1'].checked;
                    if (!chb.checked) {
                     MainGridView.rows[i].cells[0].childNodes['1'].checked = false;
                                }
               }
                 CheckBox.checked=false;

               }

               }

Select all checkbox has

  <asp:CheckBox ID="CheckBox1" runat="server" Text="Select All" AutoPostBack="true"
                                        onclick="javascript:HeaderClick(this);" OnCheckedChanged="cbSelectAll_CheckedChanged" />

and my grid is as follow :

    <asp:GridView ID="GriduwgDocuments" AutoGenerateColumns="False" runat="server" EnablePersistedSelection="true"
                            AllowPaging="True" AllowSorting="True" GridLines="None" Width="100%" PageSize="25">
                            <PagerSettings Position="Top"></PagerSettings>
                            <RowStyle CssClass="result-grid-row" />
                            <AlternatingRowStyle CssClass="result-grid-row-alternate" />
                            <SelectedRowStyle CssClass="result-grid-row-selected" />
                            <HeaderStyle Height="20px" CssClass="result-grid-header" />
                            <Columns>
                                <asp:TemplateField>
                                    <ItemTemplate>
                                        <asp:CheckBox ID="chkBxSelect" runat="server" OnCheckedChanged="cbRowChanged_CheckedChanged" />
                                    </ItemTemplate>
                                </asp:TemplateField>

                            </Columns>
                            <PagerStyle CssClass="result-grid-pager-container" />
                            <PagerTemplate>
                                <uc:GridViewPager OnPageNumberChanged="GriduwgDocuments_OnPageNumberChanged" OnPageSizeChanged="GriduwgDocuments_OnPageSizeChanged"
                                    ID="GridViewPager2" runat="server" />
                            </PagerTemplate>
                        </asp:GridView>

Could you please help me to understand what's going wrong here? TIA.