ESXi the guest OS has reported an error during quiescing

I've been messing around with Nakivo backup solution recently (which is awesome, fyi) but on one of my ESXi boxes, I got the problem Warning message on Windows Server: The guest OS has reported an error during quiescing. The error code was: 4 The error message was: Quiesce aborted..

Turns out this is due to to the ESXi box not having the correct time - I forgot to set the NTP server on this box. Set your NTP server to something like 0.uk.pool.ntp.org, wait for ESXi to update its time and try again. The error should now be gone!