The other reason a type 13 error might happen is that you've got a paragraph return in your footnote where there shouldn't be one. It's one of those characters that's only visible if you show non-printing characters. You can show non-printing characters by hitting ctrl+shit+8. Now you should see dots for every space, an arrow for manual line breaks, and the paragraph mark at the end of every paragraph.

For example:

1 some footnote text.¶
2 some more other footnote text.¶

The macro can parse the above perfectly. BUT, it will fail to parse this:

1 some footnote text.¶
2 some more¶
other footnote text.¶

That's because it will see that second ¶ mark and think that's the end of footnote 2 and will then think the next paragraph (in the example, "other footnote text.¶") is a third footnote. The reason the macro fails is because it's expecting footnotes to begin with numbers. Since the third paragraph doesn't begin with a number, there's a type mismatch.

The solution:
Hit ctrl+shift+8 to show non-printing characters and change that second ¶ (and any others like it) to a manual line break. Hit shift+enter to create a manual line break. Lines broken up with line breaks are still part of the same paragraph to word, which is why the macro will work again because now it doesn't think the third line is another footnote.