Cannot jailbreak ATV2

This ATV 2 (was formerly jailbroken) model nr. MC572NF/A with software 6.2.1 on it installed refuses to jailbreak. When I use Seasonpass I get the message that there are critical errors and seasonpass stops. Is there any soluyion for this?

Update:
Windows finds device in DFU but while uploading iBECk66apRelesase.dfu gives error entering DFU mode device not supported

Exactly the same for me. I have tried on Windows and get the same error message that the device is not supported. I mostly try on OSX platforms. I only have a recent iTunes on all platforms though, and wonder whether this is the home of the problem. When using the latest OSX release and latest iTunes on it, I get the same error message as on latest Windows and iTunes: Device not supported. On earlier OSX platforms I get stuck at " failed to reset USB count."