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FRITZ!Box reports "Authentication error occurred" when using Google calendar

The error message "Authentication error occurred" is displayed for the Google calendar on the tab "Switch Automatically" in the FRITZ!Box user interface by the profile of the smart plug, for example FRITZ!DECT 200, or the LED light FRITZ!DECT 500.


  • The FRITZ!Box's access rights to the calendar were removed in the Google account.

Note:This guide is valid for FRITZ!OS 7.50 or later. If you are using an older FRITZ!OS version, the configuration may differ or functions may not be available. You can find the FRITZ!OS version on the "Overview" page of the FRITZ!Box user interface.

1 Deleting a calendar

Before requesting access to the calendar again, you must first delete all of the Google calendars in the FRITZ!Box:

  1. Click "Smart Home" in the FRITZ!Box user interface.
  2. Click "Devices and Groups" in the "Smart Home" menu.
  3. Click the (Edit) button for the respective device or group.
  4. Click on the "Switch Automatically" tab.
  5. Click the link "Remove connections from Google calendar".
  6. Click the "Reset Google Calendar" button.
  7. Click "OK" when you are asked whether you want to delete all Google calendars from the FRITZ!Box.

Now all Google calendars are deleted and all of the smart home devices that use a Google calendar are set to manual switching.

2 Adding a calendar

  1. Add the Google calendar for the smart home device.