I think it should be:
<?php
$ProductsInRange = new WA_MySQLi_RS("ProductsInRange",$DBConnection,1);
$ProductsInRange->setQuery("SELECT * FROM products WHERE ProductManufacturerID = ?");
$ProductsInRange->bindParam("i", "-1", "".($Categories->getColumnVal("ProductManufacturerID")) .""); //ManIDParam
$ProductsInRange->execute();
?>