While upgrading the vCenter server to vCenter server version 6.7 we faced an error with the NTP configuration. Needless to say the upgrade failed and the below error was seen on the screen.

This issue comes when source vCenter is configured with external NTP server however the configuration to destination (upgraded vCenter VM) doesn’t save correctly. This is a fairly common issue while upgrading the vCenter server and the resolution is much more simpler.
Resolution
To resolve the issue follow the below action plan:
- Power off the new vCenter VM that is created as part of upgrade.
- Power on source vCenter VM.(Older vCenter server)
- Once all vCenter services are started then go to vCenter Appliance Management Appliance (VAMI) https://vCenterIP:5480
- Select Time tab, Select Mode in Time Synchronization

- Click on Edit, select Host, click OK. Now vCenter will do time synchronization from the ESXi host on which it is running.

- Perform vCenter upgrade again.
The upgrade should go through without any issues.