C# - Client-side Confirmation On Gridview Does Not Work?

In my project, In gridview i want to add a client-side confirtmation for deleting a record. Everything seems right, browser asks for confirmation, after pressing "yes", nothing happens in gridview as well at database. What's the missing point ? Also in gridview, after pressing edit button "ArgumentOutOfRangeException was unhandled by user code" exception occurs

<asp:GridView ID="grid1" runat="server" DataSourceID="sqlSource1" DataKeyNames="id"
AutoGenerateColumns="false"
BackColor="White" BorderColor="#999999" BorderStyle="Solid" BorderWidth="1px"
CellPadding="3" ForeColor="Black" GridLines="Vertical" OnRowDataBound="grid1_RowDataBound">
<Columns>
<asp:CommandField ShowDeleteButton="true" ButtonType="Image" DeleteImageUrl="~/Images/delete.gif" />
<asp:CommandField ShowSelectButton="true" ButtonType="Image" SelectImageUrl="~/Images/select.gif" />
<asp:CommandField ShowEditButton="true" ButtonType="Image" EditImageUrl="~/Images/edit.gif" UpdateImageUrl="~/Images/update.png" CancelImageUrl="~/Images/delete.gif" CausesValidation="false" />
<asp:BoundField DataField="id" HeaderText="Company ID" />
<asp:BoundField DataField="name" HeaderText="Company Name" />
</Columns>
<FooterStyle BackColor="#CCCCCC" />
<PagerStyle BackColor="#999999" ForeColor="Black" HorizontalAlign="Center" />
<SelectedRowStyle BackColor="#000099" Font-Bold="True" ForeColor="White" />
<HeaderStyle BackColor="Black" Font-Bold="True" ForeColor="White" />
<AlternatingRowStyle BackColor="#CCCCCC" />
</asp:GridView>
protected void grid1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if(e.Row.RowType == DataControlRowType.DataRow)
{
ImageButton del = (ImageButton)e.Row.Cells[0].Controls[0];
del.OnClientClick = "return confirm('Are you sure to delete ? ');";
}
}