Tip: Google Apps/"One or more of your accounts cannot be transitioned at this time"

Discovered, finally, why I couldn't transition my main Google Apps account to the new infrastructure. It turns out that if you set up another Google account as having your apps account as an alternative email address (say, for password reminders), the accounts become "linked" and the GA account email address becomes associated with an ordinary Google account.

Confused? Don't be, you probably have one other Google account, like "myname@gmail.com", and you've probably linked them in some way in the past. Do the following:

1. Log into that account, say, in gmail. Go to "Account settings"
2. Under email addresses, check to see if your GA account is listed.
3. If so, click edit, and remove it!
4. Retransition. If you've already tried to transition your entire domain, your only option is a hack. Go to https://www.google.com/a/cpanel/{yourdomain}/GoogleAccountUpgrade (where {yourdomain} is your domain, eg https://www.google.com/a/cpanel/example.com/GoogleAccountUpgrade
5. The warning will probably still appear that some of your accounts cannot be transitioned, but you should find that your account has been. If it hasn't, well, the issue lies elsewhere.

To the best of my knowledge, Google doesn't document this anywhere, and worse still their "help" on the subject is utterly useless and wrong. You can't get into the transition wizard when you transition your entire domain, and step three doesn't have the options they claim.

Hat tip to PageError, here.