Both rajkosto and InsaneNutter are correct. I think the problem is that most people don't know how their xbox 360 was jtagged. I used a variation of the aud_clamp technique ( the one that I had to solder one of the bat4 switching diode to the dvd power supply) and if I follow InsaneNutter's tutorial and used my original nand files, it won't work. However, if I use the nand I'm upgrading from, it will work. For my two cents, I think it's best if those upgrading get a backup of the current jtagged nand via boot360 and use that for the upgrade. So far doing that way seems to have the highest rate of success... @InsaneNutter: thanks again mate, you're tutorial really is very good and detailed..