was it used?, if so, someone else took it out and may have registered it.
If it was new, take it back and get another as that means that someone has aready opened it and taken it out.they also could have registered the serial for warranty purposes under their account.
It could also mean that it was was never put in the box when the wii was being manufactured.
If you can, return the bundle and get another one as that one should have a code in it.