It looks like the sprintf() that creates the necessary query is missing a formatting specifier. Using the inventory_process.php script from the downloadable source files as a reference, the statement that starts on line 133 should read:
Code:
$query = sprintf('INSERT INTO %sSHOP_INVENTORY (ITEM_NAME, ' .
'ITEM_DESCRIPTION, PRICE, ITEM_IMAGE, CATEGORY_ID) VALUES ' .
'("%s", "%s", %02f, "%s", %d)',
DB_TBL_PREFIX,
mysql_real_escape_string($_POST['name'], $GLOBALS['DB']),
mysql_real_escape_string($_POST['description'], $GLOBALS['DB']),
$_POST['price'],
mysql_real_escape_string($_POST['image'], $GLOBALS['DB']),
$_POST['cat_id']);
-Tim