I'm having a similar problem. I was using xboxhd 1.6 and it wouldn't generate the hd key from eeprom, gave a bootdecrypt error or something. I tried writing the dos locking disk and it wouldn't lock, but after one of the reboots it locked and I can't unlock it. I've tried using xboxhd 1.9 and the linux locking tools but nothing seems to get it. I have all the passwords written down from the file evox created (hdinfo.txt I think), yet none of them will unlock the drive. I've tried the master password, but I get an error that the command was rejected by the drive. I've also tried hddisab using the disable locking password, with no success.
The drive is a Western Digital 250 gig that was on the compatibility chart as being lockable (which I would think the converse should hold true as well).
Anybody have any suggestions? I'm about to take the drive back if I can't figure this thing out.