gridview events are not invoking

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VB

ASP.NET

in my project when i click on gridview to edit row , i have written rowediting event
but it not invoking in vb.net but in c#.net every thing works fine and also when click on events of gridview in properties in designer source view event name is not displaying but back end server side event is showing this is happeing in vb.net only , c# is fine. can u tell me solution?

<asp:GridView ID="gdGroups" runat="server"  AutoGenerateColumns ="false"  onrowdeleting="gdGroups_RowDeleting" 
            onrowdatabound="gdGroups_RowDataBound" onrowediting="gdGroups_RowEditing" 
            onrowupdating="gdGroups_RowUpdating" onpageindexchanging="gdGroups_PageIndexChanging"   >
            <columns>
       <asp:BoundField DataField="sno"  Visible ="false"   />
       <asp:BoundField DataField="gname" HeaderText="Group Name" />
         <asp:BoundField DataField="status" HeaderText="Status" />
          <asp:BoundField DataField="gdt" DataFormatString="{0:dd-MMM-yyyy}" 
             HeaderText="Create Date" />
              <asp:TemplateField HeaderText="Edit/Update">
                                <edititemtemplate>
                                    <asp:ImageButton ID="Image2" runat="server" ImageUrl="~/Images/icon-floppy.gif" CommandName="edit" />
                                </edititemtemplate>
                                <itemtemplate>
                                    <asp:ImageButton ID="Image1" runat="server" ImageUrl="~/Images/icon-pencil.gif" CommandName="update" />
                                </itemtemplate>
                            
                            <asp:TemplateField HeaderText="Delete">
                                <itemtemplate>
                                    <asp:ImageButton ID="Image3" runat="server" ImageUrl="~/Images/icon-delete.gif" CommandName="delete" />
                                </itemtemplate>             
  </columns>