see the follwoing code

Code:
<div class="right_txt_space_accm">
    
											<table width="100%" border="0" cellspacing="0" cellpadding="0">
											  <tr>
											  <td align=left width="100%">
                                                  <asp:GridView  AllowPaging=True   ID="GridView1" runat="server" 
                                                      DataSourceID=SqlDataSource1  DataKeyNames=userid  
                                                      AutoGenerateColumns="False" BackColor="White" 
                                                      BorderColor="#CCCCCC" BorderStyle="None" BorderWidth="1px" CellPadding="3" 
                                                      Width="449px" style="margin-right: 0px" PageSize="11">
                                                  <RowStyle ForeColor="#000066" />
                                                      <Columns>
                                                          <asp:BoundField DataField="userid" HeaderText="ID" ReadOnly="True" 
                                                              SortExpression="userid" />
                                                          <asp:BoundField DataField="Name" HeaderText="Name" ReadOnly="True" 
                                                              SortExpression="Name" />
                                                                <asp:BoundField DataField="Position" HeaderText="Position" ReadOnly="True" 
                                                              SortExpression="Position" />
                                                          <asp:CommandField   HeaderText="Select User" ShowHeader="True" 
                                                              ShowSelectButton="True"  />
                                                              <asp:TemplateField HeaderText="GFLN Member Available">
    <ItemTemplate>
        <asp:CheckBox ID="chkgfln" Enabled=false runat="server" Checked='<%# Bind("GFLN_Membership") %>' />
       
    </ItemTemplate>
       
</asp:TemplateField>
  
      <asp:TemplateField HeaderText="Approve">
    <ItemTemplate>
         <asp:CheckBox ID="CheckBox1" Enabled=true runat="server" Checked=false />
        
    </ItemTemplate>
       
</asp:TemplateField>
  

                                                       
                                                      </Columns>
           <FooterStyle BackColor="White" ForeColor="#000066" />
              <PagerStyle BackColor="White" ForeColor="#000066" HorizontalAlign="Left" />
              
              <HeaderStyle BackColor="#006699" Font-Bold="True" ForeColor="White" />

        </asp:GridView>
       
     
       
     
        								          <asp:SqlDataSource ID="SqlDataSource1" runat="server" 
                                                      ConnectionString="<%$ ConnectionStrings:reniConnectionString %>" 
                                                       SelectCommand="SELECT * FROM [Users]" ></asp:SqlDataSource>      
             								  </td>
												 </tr>
	</table>
	</div>
	
	<div visible=true runat=server id=details class="right_txt_space_accm">
	
	<asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode=conditional>

<ContentTemplate>
	<table width="100%" border="0" cellspacing="0" cellpadding="0">
	<tr>
	<td><strong>Companies </strong></td>
	</tr>
											  <tr>
											  <td align=left width="100%">
                                                  <asp:GridView ID="GridView2" runat="server" Width="286px">
                                                  </asp:GridView>
                                              </td> </tr> </table> 
                                               </ContentTemplate> 
                                           
                                             
                                             
                                                  <Triggers>
                                           <asp:AsyncPostBackTrigger ControlID="GridView1" EventName="SelectedIndexChanged" />
                                           </Triggers>
                                              </asp:UpdatePanel> 
											  
	</div>
but i m getting an exception when page(paging) is changed


Sys.WebForms.PageRequestManagerServerErrorException: Invalid postback or callback argument. Event validation is enabled using <pages enableEventValidation="true"/> in configuration or <%@ Page EnableEventValidation="true" %> in a page. For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback