Unable to Get Element with ID in VB.Net

I have the below code to retrieve the table element when the checkbox is checked.

With this, I could get the table ID. When I try to get the HtmlTable with the ID, it throws the null reference exception. Could anyone help me out?

ASPX.VB

Protected Sub CheckBox2_CheckedChanged(sender As Object, e As EventArgs)
    Dim tab As String
    Dim check As CheckBox = CType(sender, CheckBox)
    tab = check.Parent.Parent.Parent.ID
    Dim tabb As HtmlControl = Me.FindControl(tab)
    Dim myTab As HtmlTable = CType(tabb, HtmlTable)
    For Each cell As HtmlTableRow In myTab.Rows
  //My Code Here
Next
End Sub

ASPX:

<table id="itemlist" class="mel-table" runat="server">
<tr>
<td>
    <asp:CheckBox runat="server" ID="CheckBox2" OnCheckedChanged="CheckBox2_CheckedChanged" AutoPostBack="true" />
</td>
</tr>
</table>