It should be noted that Sony D21 Media is certified rated speed 16x speed Media. Whenever you attempt to overspeed the burning speed of Media faster than the certified rated speed of the Media you risk derogation the quality of the burning results.
As Forum Member troy512 asks in posting #2 do you really what to overspeed the burning speed of your Sony D21 Media?
Also it should be noted that your Nero version 126.96.36.199 of Nero v6 is not the newest most current version of Nero v6. The newest most current up to date version of Nero v6 is Nero v188.8.131.52. Suggest visiting the Nero v6 UpDate Web Link (http://www.nero.com/enu/downloads-nero6-update.php) and update your old outdated Nero v184.108.40.206 to the newer most current version of Nero v6 version 220.127.116.11.