According to the Nero Help Tool, this error is caused when a CDR formatted for packet writing is in the drive. See This cd is not writable. Please insert a writable cd
If you are using new blank unformatted disks and receiving this error, I would suspect some interference from InCD or other packet writing drivers which may be causing the disk type to be misinterpreted.
I would first uninstall any UDF reader application that is installed in Add / Remove Programs and reboot. If that doesn't help, I would then uninstall InCD and reboot. There shouldn't ever be more than one packet writing program installed, or a conflict is sure to occur.
If you try this, let us know if makes a difference.