Send GridView Row Values to Other Page With HyperLink having MasterPage using C# and VB.Net in ASP.Net

Hi!, 

I get an error "Object reference not set to an instance of an object". I only get this error when the GridView is within the ContentPlaceHolder.

I need to use this in a project that has a Master Page.

<asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
    RowStyle-BackColor="#A1DCF2" AlternatingRowStyle-BackColor="White" AlternatingRowStyle-ForeColor="#000"
    runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:BoundField DataField="Id" HeaderText="Id" ItemStyle-Width="30" />
        <asp:TemplateField>
            <ItemTemplate>
                <asp:Label ID="lblName" runat="server" Text='<%# Eval("Name") %>' />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:BoundField DataField="Country" HeaderText="Country" ItemStyle-Width="150" />
        <asp:TemplateField>
            <ItemTemplate>
                <asp:LinkButton ID="lnkDetails" runat="server" Text="Send Details" PostBackUrl='<%# "~/DetailsVB.aspx?RowIndex=" & Container.DataItemIndex %>'></asp:LinkButton>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    If Me.Page.PreviousPage IsNot Nothing Then
        Dim rowIndex As Integer = Integer.Parse(Request.QueryString("RowIndex"))
        Dim GridView1 As GridView = DirectCast(Me.Page.PreviousPage.FindControl("GridView1"), GridView)
        Dim row As GridViewRow = GridView1.Rows(rowIndex)
        lblId.Text = row.Cells(0).Text
        lblName.Text = CType(row.FindControl("lblName"), Label).Text
        lblCountry.Text = row.Cells(2).Text
    End If
End Sub

Please assist.