This log message means that updating the real time clock (RTC) with thetime received from the NTP server has failed at that instant. This could be a temporary issue and RTC clock can be updated successfully a bit later. But then the message shouldn't be seen any more. If the message log is persistent, it can mean that there is an issue with the synchronization of RTC clock and time received from NTP server.
You can check "show ntp status" and "show ntp associations" for the polling status.
Hope this helps.
Regards,
-r.
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