It is how the NTP (Network Time Protocol) service works. There are different layers (Strata) of servers, with the national time service ones at the top, secondary ones below them etc. The service is a peer-to-peer service. A PC/server looks for a time server which must be either in a higher stratum or, at worst, a peer. It cannot be at a lower stratum.
It would seem, from your error message, that the server you are trying to link to is reporting that it is in a lower stratum, so the service is, correctly, denying the connection.
The fault would seem, therefore, to either that your PC has an inflated idea of itīs level or the service is pointing at the incorrect server.
See if
this helps to sort it out.