Here is Nespresso's answer. Didn't work for me.
1. Unlock and open the top of the machine and eject the capsule, if necessary
2. Unplug the machine.
3. Close and lock the top of the machine and plug in.
4. Use either a stopwatch or an app that allows you to set a timer for 35 seconds.
5. Tap the button to turn the machine on.
6. As soon as the light comes on, press and hold the button from the side.
7. Hold the button until the light becomes steady. Once steady, immediately lift the finger.
8. Activate your timer you set for the 35 seconds.
9. When the time is up immediately press the button 5 times as quickly as possible.
10. The light should then blink slowly. After 15 seconds, the light should go steady if error is cleared properly.