Problems Promoting OS X Server to PDC Role: Fixed

When trying to promote my Xserve from a Standalone to PDC (because I have Mac and PC clients) it pops up and asks you for your password, but with YOUR LONG USERNAME FILLED IN.

You have to change it to 'diradmin' and use THAT password. Very frustrating. The statement it gives 'Error while writing settings (Cannot make the server a Windows pdc)' is less than informative if you use just the administrator's password.

How about telling me I need to use the 'diradmin' account to make this change?

That would be nice. Shame Apple, you're supposed to make this easier. Yeah, it's more secure to not even tell me the password is wrong, but very annoying.

Notice also that it asks for an administrator's password, but it really wants diradmin's password.

Welcome googlers, I hope it helped you. Took me a bit of keyword searching (namely the error message) to find this one.