First of all, make sure this device is recognized as a SCSI device. (Have a look inside /proc/scsi/scsi: You should be able to see it listed in this file). Secondly, add RW permission for user to the corresponding sg device file. The problem is that cdrecord is maybe running suided root and your device file is not writeable for the user.

Finally, make sure that the device is not used by any other applications when using it (not mounted or anything else).