I can write to dvd but not cd

I find that although I can write DVD’s just fine, I cannot write to a CD. I have both an internal and an external burner on this machine, but I can’t write a Cd. I am particularly (tho not exclusively) trying to copy a book my wife bought online to CD’s for her. The first one worked fine, then nothing! I’ve reinstalled the OverDrive Media Console and updated permissions. Now I can’t even write using Nero. Any ideas?