According to the Haynes Manual it's "Code from key not recognised by immobiliser transceiver".
Presuming you haven't got both keys on the same ring (which could cause interference), try using the other one to see if there's a problem with the one you're using.
Presuming you haven't got both keys on the same ring (which could cause interference), try using the other one to see if there's a problem with the one you're using.