Nero is actually "smart" about what serial you enter. There are only to ways to get access to recode.
The first is to use the reloded demo, on a fresh install without entering a serial.
The second is to buy nero ultra for $100 in the store.
If you updated an older Oem nero, you can't use recode. Nor if you use an oem serial, nero will actually reinstall itself with different options depending on the serial # used.