BeagleBone Enhanced RTC (PFC8563)

I’m trying to get the RTC module of my BBE working. I found this tutorial from SanCloud, but when I give:

echo pcf8563 0x51 > /sys/class/i2c-adapter/i2c-0/new_device

I get

[  272.496711] rtc-pcf8563 0-0051: pcf8563_write_block_data: err=-121 addr=0e, data=03
[  272.515598] rtc-pcf8563 0-0051: pcf8563_probe: write error

I also try adding


to /boot/uEnv.txt, but with the same results.

What does the error mean? Am I missing something obvious?