Trouble with UPC/EAN codes

I am using Nero Reloaded and want to create an audio CD. To better recognize my disks, I usually put a customized UPC/EAN code on them. For example, the first 8 numbers are the date (14102004 = 14/10/2004) and the other are a unique ID I assign to my disks. I store them on a database into my machine so I can always identify them :wink:

Since I installed Nero it tells me the code is not valid. Do I have to meet some standards to create one ? :a