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.