It still gives me the same error message after moving the code, and multiple records don't show up in the select list. It also doesn't show the appropriate sizes for each product.
SELECT *
FROM Prod INNER JOIN ProdType ON ProdType.TypeID = Prod.ProdType INNER JOIN ProdSize ON Prod.ID = ProdSize.ProdSizeID INNER JOIN ContSize ON ProdSize.ContSizeID = ContSize.ContID
WHERE ID = colname
GROUP BY ID
colname type: integer
default value: -1
run-time value: $_GET['ID']
File attached.