Can't get flash install to work

Latest aTV Flash, ATV upgraded to 2.1.

The creation of the flash drive seems to go OK, but when I power off the ATV, insert the flash drive, and power on again, I don’t get the response described in the doco. The ATV boots normally, I get no request for confirmation of install, etc. Basically, it appears that the flash drive is ignored.

I’ve tried this with both an 8GB flash drive and a 100GB USB drive, both freshly formatted (the latter with just one small partition).

Is it necessary that it be a flash drive, or can it be any USB drive. Does the size of the partition make any difference?

Thanks and regards,

ATV is not compatible with a lot of flash drives, read this post for compatible flash drives.