Xbox auto-shutdown query

Hi, I have some issues with the xbox while doing ftp. Basically, I can transfer files with no issues at all but when transferring large files over a long period (e.g 4-5 hrs),the xbox auto shutdowns itself for no apparent reason. I tried using unleash x and xbmc but both have the same issue. I made sure to check that the auto-shutdown is not turned on for either dash. My ftp client on my pc is flash xp. While transferring overnight large files, the xbox auto-shutdown while ftp and corrupted my hdd data which I have resorted to reformat it and restart. So, my qs is if anyone may know why the xbox does this or does it auto-shutdowns perhaps for long idle time, or maybe file transfer have reached a certain limit or perhaps the xbox itself have a file limitation to what can be transferred. Any help on clarifying this weird shutdown issue would be great. Thanks in advance