You still haven't said the exact error you're getting, but if you're having trouble in an existing document but it works in new documents, see Debugging Broken Documents.
Restart Zotero, and then, with Word closed, try reinstalling the Word plugin from the Cite pane of the Zotero preferences. If you still get an error in a completely new document, provide another Report ID.
Do you get an error in a new document when inserting citations or only when trying to insert a bibliography? Do you have track changes enabled or any not accepted/rejected suggested changes?
See Steps to Reproduce.
[JavaScript Error: "The operation couldn't be completed. (OSStatus error -1708.) @[selectField:field.m:341]" {file: "file:///Applications/Zotero.app/Contents/Resources/extensions/zoteroMacWordIntegration@zotero.org/components/zoteroMacWordIntegration.js" line: 217}]
version => 5.0.66, platform => MacIntel, oscpu => Intel Mac OS X 10.13, locale => en-US, appName => Zotero, appVersion => 5.0.66, extensions => Zotero LibreOffice Integration (5.0.14.SA.5.0.66, extension), Zotero Word for Mac Integration (5.0.18.SA.5.0.66, extension)