To upgrade vCenter Server on a Windows virtual machine or physical server, your system must meet specific hardware and software requirements.

Synchronize the clocks on all machines running the vCenter Server 5.x services. See Synchronizing Clocks on the vSphere Network.

Verify that the system network name of the machines running vCenter Server 5.x services are valid, and are reachable from other machines in the network.

Verify that the host name of the virtual machine or physical server that you are installing or upgrading vCenter Server on complies with RFC 1123 guidelines.

If your vCenter Server service is running in a user account other than the Local System account, verify that the user account in which the vCenter Server service is running has the following permissions:

Member of the Administrators group

Log on as a service

Act as part of the operating system (if the user is a domain user)

Verify that the LOCAL SERVICE account has read permission on the folder in which vCenter Server is installed and on the HKLM registry.

Verify that the connection between the virtual machine or physical server and the domain controller is working.