Hello,
That's a generic error from ZipArchive PHP when the file can't be created. The most common source of this problem is missing write access to the temp folder or an open_basedir restriction:
We recommend you to check your server config. Maybe it's not using /tmp as default temp folder or you have some open_basedir restriction. Or you are trying to save the DOCX in a not existing folder:
http://php.net/manual/en/ziparchive.close.php
Regards.