Well, it is really tough not knowing why it isn't working. I have attached the factoryReset file from the Mitel KMS article. However, an empty one should have worked just the same. This file just has the steps if you open it in Notepad++ for example.
What else can you do?
Try different USB drives
Try the process on a working (6.0 or >) RFP to see if you can get it to work.