Hello,
sysprep doesn't join the computer to the domain. Sysprep does only the following: generalize, sid gerenation, run script to install video card, install drivers, install various program (window security essential), configure keyboard because microsoft never understood what is French Canada => French Canada keyboard and always put English Canada => French Canada without removing all other keyboard, install ghost agent. It also generate a computer name, which is randomly generated from sysprep.
Then, configuration task give the computer name and domain join, but only after the sysprep process. Everything is working well on my other images, just this one that started doing that problem.
But then, It got worst. Here's the situation:
I deploy the computer, sysprep is ran, computer is logged as administrator, installation script execue, ghost client is installed then the computer wait for further information from ghost. The, the configuration task is run, computer reboot in winPE, it receive his name, reboot and join domain (from task log). But in reality, the computer only changed name, no configuration task.
Since that, the computer has rebooted many time (from users trying to login). 24 hours later, I try a new configuration task from cold boot. It does all the task as it suppose but no domain join (although log says it did). Another day after, tried again, same problem. I then proceed to connect myself as administrator and join the computer to the domain manually and it work.
I'm currently deploying the images on another computer in another network to see if the same problem exist.