I don't know. The best i can think of is an update in your Nero or burner firmware or both. Someone else might have an idea.

I presume it is a blank disk in the burner right? It sounds like the program is having difficulty recognising the burner or burner recognising the disk. I presume you're using a good brand CD-R & not some cheap muck made in China or Taiwan. Some brands don't work well in some burner brands/models.

Note: I presume you saw this Burning an audio CD from your MP3's