So I guess gmaxey tried to point me to the problem:

But apparently I was too dense to take the hint.
When I try to run the macro in the link above it generates 6 (empty) dynamic footnotes (there are nearly 500 footnotes in the document) and exits with run time error 4605.

I assume that my lack of knowledge concerning VBA must be annoying to some of you. But I have been spending an awful lot of time working on the document for the past months only to notice now that there are no dynamic footnotes -- which is a requirement of the publisher that I have to submit the manuscript to in 12 days.
My bad, of course.
Any help to get those footnotes behaving like regularly generated Word footnotes would be most appreciated.