Error getting values from a table created dynamic!

[renateves]

My problem is that i have a xml file that is convert into a table (by
xsl) in a
aspx file, and in vb code i want to get and put some values to the
table. Is the code:
ASPX FILE
<Get the table with the values from the xml file>
.....
<asp:Xml id="myXml" DocumentSource= "XMLCat.xml "
TransformSource ="Perf.xsl" runat="server"> </asp:xml>
.....
XSL File
<xsl:styleshe et version='1.0'
xmlns:xsl='http ://www.w3.org/1999/xsl/transform'>
<xsl:template match="/">
<style>
.value { width:"25%";fon t-family:courier new; font-size:.8em;
white-space=pre;}
</style>
<table border="1" cellspacing="0" cellpadding="3" id="tablexml">
<tr>
<th>id</th>
<th>text</th>
</tr>
<xsl:for-each select='treenod es/treenode'>
<tr>
<td class="value">< em><xsl:value-of
select='@id'/></em></td>
<td class="value">< xsl:value-of select='@text'/></td>
</tr>
<xsl:for-each select='treenod e'>
<tr>
<td class="value">< em><xsl:value-of
select='@id'/></em></td>
<td class="value">< xsl:value-of select='@text'/></td>
</tr>
</xsl:for-each>
</xsl:for-each>
</table>
</xsl:template>
</xsl:stylesheet>
VB FILE
.....
tc.Controls.Add (New LiteralControl( newID & "," & category))
tr.Cells.Add(tc )
tableXml.Rows.A dd(tr)
.....

and the output error is:

Exception Details: System.NullRefe renceException: Object reference not
set to an instance of an object.

Source Error:
Line 153: tc.Controls.Add (New LiteralControl( newID &
"," & category))
Line 154: tr.Cells.Add(tc )
Line 155: tableXml.Rows.A dd(tr)
Line 156: Else
Source File: C:\Inetpub\DSL\ Patrocinio.PT\P ortalDSL\Deskto pModules\FAQ\As kManag.aspx.vb
Line: 155

Stack Trace:
[NullReferenceEx ception: Object reference not set to an instance of an
object.]
ASPNetPortal.As kManag.insertNe wNodIntoTable(S tring newID, String
category, String id) in
C:\Inetpub\DSL\ Patrocinio.PT\P ortalDSL\Deskto pModules\FAQ\As kManag.aspx.vb: 155
ASPNetPortal.As kManag.cmd_AddC ategory_Click(O bject sender,
EventArgs e) in C:\Inetpub\DSL\ Patrocinio.PT\P ortalDSL\Deskto pModules\FAQ\As kManag.aspx.vb: 64
System.Web.UI.W ebControls.Link Button.OnClick( EventArgs e)
System.Web.UI.W ebControls.Link Button.System.W eb.UI.IPostBack EventHandler.Ra isePostBackEven t(String
eventArgument)
System.Web.UI.P age.RaisePostBa ckEvent(IPostBa ckEventHandler
sourceControl, String eventArgument)
System.Web.UI.P age.RaisePostBa ckEvent(NameVal ueCollection postData)
System.Web.UI.P age.ProcessRequ estMain()

Thanks for the help that can be give!