[O] footnotes problems in split files on export to latex

[Sharon Kimble]

I have a very large file that I'm working on into 4 sections and have
included the sections like this, in the middle of the main file -

--8<---------------cut here---------------start------------->8---
#+include: "~/research/drugs/drugs17-a2i.org"
#+include: "~/research/drugs/drugs17-k2n.org"
#+include: "~/research/drugs/drugs17-o2z.org"
--8<---------------cut here---------------end--------------->8---

And moved the footnotes for each new section over to the relevant #+include: 
file.

Now when I try to export to latex it replies with this error message -

--8<---------------cut here---------------start------------->8---
(user-error "Definition not found for footnote -4-83") in user-error
--8<---------------cut here---------------end--------------->8---

How can I surmount this problem please?

Thanks
Sharon.
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