Select categories / folders applet is failing to start

If category / folder selection applet fails to start, as shown on the image below, most commonly this error is caused by disabled Java applets.

How to enable Java applets

1. In Lotus Notes, select "File" -> "Preferences".

2. In "Preferences" window, select "Basic Notes Client Configuration" section.

3. In "Basic Notes Client Configuration" -> "Additional options", put a check-mark on "Enable Java applets".

4. Press "OK".

5. Restart Lotus Notes.