JabRef has been evolving quite a lot, especially in the past year. Hence, I believe the current help file about EndNote is outdated (http://help.jabref.org/en/EndNoteFilters). Do you confirm?
There was no answer. I have problem with that, too.
Using (not with my free will) EndNote X8 and tried to import a JabRef 3.8 BibLaTeX file using the BibTeX-Import-Filter from EndNote. The result is 0 but there are no error messages.