[JavaScript Error: "*** -[__NSDictionaryM setObject:forKey:]: object cannot be nil (key: /Applications/Microsoft Word.app/ 1) @[getDocument:application.m:204]" {file: "file:///Applications/Zotero.app/Contents/Resources/extensions/zoteroMacWordIntegration@zotero.org/components/zoteroMacWordIntegration.js" line: 404}]

This could happen if you used the Zotero beta and switched back to the release version.

Try reinstalling the Word plugin from the Cite → Word Processors pane of the Zotero preferences, and then restart Word.

If that doesn't help, remove Zotero.dotm from your Word Startup folder, restart Word to confirm that the plugin is completely gone from Word, and then try the plugin reinstall again.