On following your advice, I immediately got a very helpful alert saying
(roughly, from memory):
Line: 1
Char: 1
Object required
So now it begins. The first script tag included XWiki's skins.js, but I
don't see anything there that would provoke such a complaint. My guess
is that it would be caused by a reference to an attribute on an
undefined object. More than that, it didn't show on another document,
so on we go...
brain[sic]