I have got the very same error... But on an internal burner!! Can't figure out what it is! But since you're running an external, try this. There you go! If you do a search on SCSI Command Errors, you will find that many others have had the same issue as yours with USB Recorders, regardless of the software used. Meaning, it occurs with Nero, CD Creator, RecordNow, etc. And the error message varies from SCSI Command Error, Bus Rest, etc... In most cases, users have found that updating the drivers for the USB Controller resolves the issue. Other found a new External Chassis for the Recorder resolved the issue. And we provided a work around in our MMC.DLL file that causes our software to reissue the command till the recorder is free and accpets, instead of timing out so soon after a lack of response from the device. This resolved the issue for some, but not for others. This MMC.DLL file is part of Nero 6.6.0.3 and above builds. Try to disconnected all USB devices except for the external DVD burner. As a last resort, after trying the above solutions and others, they finally connect as an internal to the system and all issues are resolved. Hope this helps...
