Following are scenarios where the error "Unknown error occurred" can appear in the YubiKey Personalization Tool, as well as guidance on what to do in each case.

macOS

You receive the error "Unknown error occurred" in the YubiKey Personalization Tool with your YubiKey plugged in

Beginning in macOS Catalina, Apple included a new security feature that requires the YubiKey Personalization Tool to be granted Input Monitoring permission before it will be able to communicate with YubiKeys. To clarify, the YubiKey's OTP application, which is what the YubiKey Personalization Tool interacts with specifically, works essentially like a USB keyboard, which is why Input Monitoring permission is needed. To grant the YubiKey Personalization Tool this permission:

1. Quit out of the YubiKey Personalization Tool completely by clicking YubiKey Personalization Tool > Quit YubiKey Personalization Tool, or pressing ⌘+Q on your keyboard with the YPT window in focus.
2. Open System Preferences.
3. Click Security & Privacy.
4. Click the Privacy tab.
5. Scroll down until you see Input Monitoring and select it.
6. Click on the padlock in the lower-left corner and authenticate so you are able to make changes.
7. Click the + button.
8. In the window that appears, select Applications in the left column if it is not already selected, then scroll down to and select YubiKey Personalization Tool. Click Open.
9. Make sure YubiKey Personalization Tool now appears in the list of apps with Input Monitoring permission with its box checked.
10. Click the padlock again to prevent further changes.

Once this has been done, after reopening the YubiKey Personalization Tool, you should no longer receive the error message, and be able to configure your YubiKey's OTP application. If you still see the message however, move on to the next section.

Any OS (Windows, macOS, Linux, etc.)

You receive the error "Unknown error occurred" in the YubiKey Personalization Tool with your YubiKey plugged in

Since the YubiKey's OTP application, which is what the YubiKey Personalization Tool interacts with specifically, works like a USB keyboard, pieces of software that modify keyboard operation (examples listed below) can interfere with the Personalization Tool's ability to communicate with the YubiKey, resulting in the aforementioned error. If you discover that this error is caused by an application that is not listed below, please feel free to let us know by clicking Send us feedback on this article at the bottom of this page, and fill out the form.

• Karabiner-Elements
• Keyboard Maestro
• Razer Synapse
• KeyCue
• Typinator
• Rocket
• Rambox
• TextExpander

For more information, including how to work around the issue when using some keyboard-altering applications, please see https://github.com/Yubico/yubikey-personalization-gui/issues/25.