In the case of the Yamaha CDR 400, the Code 04 error is similar to a buffer underrun. Some general info on buffer underruns:During disc write, the buffer of the CD recorder is constantly being fed with data via the SCSI bus. If anything interrupts this data flow long or frequently enough that the buffer empties, such as the thermal recalibration of your hard drive, a buffer underrun will occur, and the disc will be ruined.If you experience a buffer underrun, please check the following:1) Remove any items which may be detrimentally affect the data flow of the SCSI bus, such as INITs and Extensions that come with the CD recorder, other CD-ROM, CD-R or SCSI polling extensions.2) Ensure AppleTalk is off.3) Try using an image file to create the disc.4) For Pro Tools III and Session 8 systems, move your hard disk to your Macintosh SCSI bus. MasterList CD does not take specific advantage of these SCSI cards, and playing files from a drive connected to them may actually slow the performance of the disc writing feature. In most cases the Macintosh SCSI bus will be faster as the data travel will be confined to a single SCSI bus.