Andrew I just tried this myself. Launched an instance. Logged on, went through the initialization dialog with the six items. Then logged on from my desktop system with the admin username and password, and got through. I was hoping I'd get the error you got and be able to fix it.
Unless I can reproduce it there's not much I can do...
Suggest you terminate this instance and launch another instance and hope this time you have the experience I had.
Please report back the result. And sorry for the problem.
Dave