You aren't the only one. It's very frustrating for what should be a straightforward task.
And McAfee supports solution is, just install from scratch and migrate the machines separately. They didn't seem interested in getting to the bottom of the issue. I haven't yet tried this as I haven't had time. Did you manage to fix yours?
Unfortunately not. I ended up connecting the two EPO servers and using the Transfer Systems function to move all my clients over. Luckily I do not have a complex tree and only a few policies.
I believe I have cracked it!
On mine at least
I went back to the very start to look at where I might have gone wrong and noticed that when I first created the migration file I accepted the default path to the ePO server (https://localhost:8443), so instead changed local host to the server name. Re-created the migration file and went back to my new server. Now my new server had an agent and virus scan installed and running (during the previous install attempt I just stopped all of the services) so I decided as a secondary step just to completely remove all McAfee products from this server.
Ran the migration import and then setup and it worked first time, no complaints about the username and password.