The reason why your LJ feed isn't working is because someone must've
changed the settings so now LJ is trying to read your Journal page
(http://www.neilgaiman.com/journal/journal.asp), instead of the RSS feed
(http://www.neilgaiman.com/journal/blogger_rss.xml), and is finding the
former unreadable (hence the RSS parser error message). Let's see if we
can get the folks over at LJ to fix it..
Which is an enormous relief, as I was sure I'd broken something. Here's hoping someone can fix it. (We didn't create the officialgaiman link, and can't do anything to change it...)
... and, as if by magic, Krissy from Livejournal has just offered to help, and to be this journal's Livejournal contact for when things go wrong. I have gratefully accepted.