I've noticed that the English Wikipedia is spitting out this error
message in place of the <references/> tag when there are no <ref> tags
anywhere in the article.
This is a new development, I believe? In the past I've sometimes thrown
a <references/> tag (or more specifically the {{reflist}} template) into
an existing references section even if there weren't currently any
inline references in the article, since I just as often put <ref> tags
into articles while neglecting to add a <references/> and wanted to make
things easier on future editors who might make the same oversight. I'm
not sure why this counts as an error now. Is it intentional?