change 1

$sord = $_GET['sord'];

INTO

$sord = 'invid';

change 2

$SQL = "SELECT invid, invdate, amount, tax,total, note FROM invheader ORDER BY $sidx $sord LIMIT $start , $limit";

INTO

$SQL = "SELECT invid, invdate, amount, tax,total, note FROM invheader ORDER BY $sidx , $sord LIMIT $start , $limit";

The XML error now be this :

XML Parsing Error: junk after document element
Location: http://localhost/SpDatabase/res/grid/
Line Number 62, Column 1:<?xml version='1.0' encoding='utf-8'?><rows><br><page>1</page><total>1</total><records>1</records><row id='1'><cell>1</cell><cell>2001-01-10</cell><cell>103.00</cell><cell>45.00</cell><cell>149.00</cell><cell><![CDATA[This is record 1]]></cell></row></rows>
^

here is the output

XML Parsing Error: junk after document element
Location: http://localhost/SpDatabase/res/grid/
Line Number 62, Column 1:<br />
^

and here is the code of file index.php

http://pastebin.com/cTDyPsyR

What do you think is going wrong ?

Thanks.