More info: the stuff I've found by searching, says to remove it as a subdomain. Done; I now have no subdomains, no parked domains, nada... and still get the same error. However, the domains and subdomains still appear in some of the dropdown boxes for assorted options! Some of the things I've found say that if that happens, the cure is to remove it manually from assorted files, using root shell access, but of course I don't have that, so it will require manual intervention from the staff.
Also, I'm thinking it MIGHT have something to do with the fact that I do already have DNS set up... using nameservers *elsewhere*. Would dumping those help? That would make the process more painful, as there are reasons I'm not using x10's nameservers. (Mainly, in order to host my email at certain other places, which I had to do since x10 disabled my catchall, I had to be using the other places' nameservers. That's a whole 'nother story. Don't get me started.)
Tell ya what, guys, since all my content so far is just static stuff that I've got on my own HD in an identical structure, maybe you could just zap my account and reinstall it like it was brand-new? I'll re-upload all my own files.