For the time being, documents saved in the format .docx will cause an error when formatting the document in Writ-N-Cite for Mac. Instead, please save the document in the older .doc format, which gives no problems until the problem has been solved.
For your information, RefWorks has launched a new version of Write-N-Cite vers. 4 for Mac. You can download this through your RefWorks account under “Tools” –> Write-N-Cite.