Because of recent Windows 10 updates in Office 2016, 2019 or Office 365, when you press the Add/Edit ribbon button in the JChem ribbon, with default Microsoft Office settings you will receive this error message:
The solution is the following:
1. Go fo File/Options/General menu.
2. Change the default option: "Optimize for best appearance" to "Optimize for compatibility"
3. Please note that you have to restart the application.