I am trying to record

I am trying to record from an old Sony compact disc player, model CDP-C445 to my Sony MDS-JE480 Mini Deck. I have the optical in on the mini disc player going into the optical out on the CD player. The error message on the mini deck says C71/Din Unlock. Why won't the CD, which is a wave file that I downloaded from my computer, record onto the mini disc. I am able to record using the analog in on the mini deck to the analog out on the CD player, but thought I'd get better quality using a digital connection. Please help...