I worked as a member of the design team on most of the HDD->Firewire chips made in the last 6 years! Chances are that enclosure has a chip I worked in inside it. If it is PATA->FW then it is likely to be an Oxford Semiconductor 911+
Let me know which enclosure it is. If it is one of ours I can try it here.
There is always a chance it is an early one with a bug in the firmware