"Please post a link to the page causing the 404 error."
My initial post contained details of the exact page. The submit button on profile edit. Not difficult to find if you're familiar with your own site.
But then I also received a 404 on my initial attempt to reply to this. A refresh fixed it. That would point to a deeper, server config or url parsing related issue. But then you presumably sorta have tech guys, so I won't try to do their job by guessing possible causes.
A slight side note - others are also reporting profile edit issues in other threads, so apparently my problem was not isolated.

