I have a problem regarding gridview............

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" 
           CellPadding="3" ForeColor="#333333" GridLines="None" 
     CellSpacing="4" Width="92%"  Visible="False" BorderColor="#DEBA84" 
           BackColor="#DEBA84" BorderStyle="None" BorderWidth="1px" AllowPaging="True" 
           onpageindexchanging="GridView1_PageIndexChanging" DataKeyNames="P_id" 
           onrowdatabound="GridView1_RowDataBound" 
        >
     <columns>
        <asp:BoundField HeaderText="Username" DataField="Uname" />
        <asp:BoundField HeaderText="Product name" DataField="Product_name" />
        <asp:BoundField HeaderText="Product Quantity" DataField="Product_quan"  />
        <asp:BoundField HeaderText="Delivery Date (MM/DD/YYYY)" DataField="Delivery_date" />
        <asp:BoundField HeaderText="Extend Date (MM/DD/YYYY)" DataField="Extend_date" />
        <asp:BoundField HeaderText="Product Information" DataField="check_bit"  />
        <asp:TemplateField>
        <itemtemplate>
        <asp:LinkButton ID="click" runat="server" Text="Dispatch">
        </itemtemplate>
         <asp:TemplateField>
        <itemtemplate>
          <asp:LinkButton ID="lnkbtn" runat="server" Text="InvDisp" ForeColor="Blue">
        </itemtemplate>
    </columns>
        <footerstyle backcolor="#990000" font-bold="True" forecolor="White" />
        <pagerstyle backcolor="#FFCC66" forecolor="#333333" horizontalalign="Center" />
        <SelectedRowStyle BackColor="#FFCC66" Font-Bold="True" ForeColor="White" BorderColor="#738A9C"  />
        <HeaderStyle BackColor="#A55129" Font-Bold="True" ForeColor="White" Height="30%" />
        <alternatingrowstyle backcolor="White" />

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
        {
            if (e.Row.RowType == DataControlRowType.DataRow)
            {
                DataRowView row = (DataRowView)e.Row.DataItem;
                string eid = ((LinkButton)e.Row.FindControl("click")).Text;
            
                string lnkbtn = ((LinkButton)e.Row.FindControl("lnkbtn")).Text;
                string param = "challan_report.aspx?P_id=" + row["P_id"] + "&Uname=" + row["Uname"];
                ((LinkButton)e.Row.FindControl("click")).Attributes.Add("OnClick", "window.open('" + param + "','PopupWindow','toolbar=no, location=no, directories=no,titlebar=no, status=no, menubar=no,resizable=NO,scrollbars=NO,copyhistory=no,width=600,height=600,top=20,left=20')");
                string caram = "Invoice.aspx?P_id=" + row["P_id"] + "&Uname=" + row["Uname"];
                ((LinkButton)e.Row.FindControl("lnkbtn")).Attributes.Add("OnClick", "window.open('" + caram + "','PopupWindow','toolbar=no, location=no, directories=no,titlebar=no, status=no, menubar=no,resizable=NO,scrollbars=NO,copyhistory=no,width=600,height=600,top=20,left=20')");
                
            }


        }