Microsoft JScript runtime error:

[Suresh K]

Hi
   I am using one Hierarchy Grid to display data.

<telerik:RadGrid ID="Grdaccountdraftavail" runat="server" AllowPaging="True" AllowMultiRowSelection="True"
                            ShowFooter="true" Skin="Office2007">
                            <PagerStyle AlwaysVisible="true" />
                            <MasterTableView Caption="<table style='background-color:Silver; width:100%; color:Black;text-align:center;'><tr><td>Accountwise Draft Availability</td></tr></table>"
                                DataKeyNames="Accountid">
                                <Columns>
                                    <telerik:GridClientSelectColumn UniqueName="Grdaccountdraftavail_select">
                                        <HeaderStyle HorizontalAlign="Center" Width="20px" />
                                        <ItemStyle HorizontalAlign="Center" Width="20px" />
                                    </telerik:GridClientSelectColumn>
                                </Columns>
                                <ExpandCollapseColumn Visible="True">
                                </ExpandCollapseColumn>
                                <DetailTables>
                                    <telerik:GridTableView Name="Providers" runat="server">
                                    </telerik:GridTableView>
                                </DetailTables>
                            </MasterTableView>
                            <ClientSettings EnableRowHoverStyle="true">
                                <Selecting AllowRowSelect="true" />
                            </ClientSettings>
                        </telerik:RadGrid>

I am trying to Expand it is expanding first time only after that it's not working. it showing the message like this "Microsoft JScript runtime error: Sys.WebForms.PageRequestManagerServerErrorException: Object reference not set to an instance of an object".

Can any body help me  to resolve this problem.

Thanks
Suresh K