Error: "This operation is not allowed in the current state as operation 'None' is already in progress." when attempting vCenter Stage 2 Pre-upgrade check

Products

• VMware vCenter Server
• VMware vCenter Server 7.0
• VMware vCenter Server 8.0
• VMware vCenter Server 6.0

Issue/Introduction

Stage 2 pre-check of vCenter upgrade fails with the error:

Pre-upgrade check failed due the following problem: This operation is not allowed in the current state as operation 'None' is already in progress.

Cause

The issue can occur when the source vCenter is unable to contact the configured NTP servers or when the newly deployed vCenter has restrictions with the firewall rules.

Resolution

• Login to the source vCenter's VAMI page: https://<Source_vCenter_FQDN>:5480
• Check for NTP configuration errors
• Disable NTP or fix communication to the NTP servers. If NTP is already disabled, please also remove "server ###.###.###.###" from /etc/ntp.conf if any server entries exist.
• Ensure DNS is working
  • Check forward and reverse lookup for the vCenter Server
• Check if the necessary ports and access has been provided at the firewall level for the new vCenter IP
  • This includes, but not limited to allowing TCP port 443 from the temporary vCenter IP address to the ESXi host where the VM resides on
• Re-run Stage-2 pre-checks

Note : To avoid upgrade or install failures in vSphere 8.0, your DNS server must comply with RFC 4074 behavior for negative AAAA responses:
It must return RCODE = 0 and an empty answer section for AAAA queries when there is no IPv6 record, rather than NXDOMAIN or other errors.