Hi Jason, thank you for your tip. You were right, our item numbers are alpha numeric. Also I added the code you posted, and everything works.
There is another question you maybe able to help me with.
On the confirm page I had to add the fields company and department to invoice and shipping information. The little check box "same as" is supposed to copy the information from the invoice info to the shipping info. But it doesn't work for the two new fields I added. Would you know where I have to change the code to make this happen?