Hi Basj, thanks for the quick reply.
Yes, I can confirm that Fences 4 is listed when I go to My Account -> My Downloads -> Object Desktop Manager -> Individual Downloads. I have been able to install it via Object Desktop and it runs. The only issue is with activation.
I saw the article that said that error -205 could be caused by non-Western characters in the computer's name, and I've checked that this is not the case.
My original copy of Fences 3 was purchased a long time ago under a different account, or possibly even as a guest, and I don't have access to the associated email address any more. It's certainly not associated with my current email address so I was wondering if clearing a registry key somewhere might fix the issue -- it looks like I've got the right to run Fences 4 but something in the system is remembering my old Fences 3 information so it's getting confused when I try to register Fences 4. I don't want to go digging in my registry if there's an easier fix though.