Lines 44-51 should be updated to:
if (isset($_GET["Search"])) {
$WADbSearch1 = new FilterDef;
$WADbSearch1->initializeQueryBuilder("MYSQL","1");
//keyword array declarations
//comparison list additions
$WADbSearch1->addComparison("ProductSKU","".$_GET['ProductSKU'] ."","AND","=",0);
$WADbSearch1->addComparison("ProductName","".$GET['ProductName'] ."","AND","=",0);
This issues are that you set the trigger to be "any form post" and the search form doesn't use a post method. So I switched it to look for the submit button in the GET type form.
The other issue is that you had set the two columns to filter with the values from the Recordset... you need to filter the recordset with the values from the form. You never told the search what the form elements were to search from.