This issue occurs if the source vCenter Server Appliance 5.x is using localhost.localdom for the hostname. The certificates were created using this hostname and fails on vCenter Server 6.0.
Resolution
To resolve this issue, replace the certificates on the source vCenter Server Appliance 5.x or replace the certificates that vCenter Server Appliance 6.0 is using.
To replace the certificates on the vCenter Server Appliance 5.x prior to upgrade:
Shut down the destination vCenter Server Appliance 6.0.
Power on the source vCenter Server Appliance 5.x.
Log in to the Administrator Web Interface at https://vCenter_Appliance_FQDN:5480/.
Click the Network tab and click Address.
Change the hostname and click Save Settings.
Note: You cannot change the hostname if the appliance uses DHCP to obtain an address.
Click the Admin tab.
To regenerate the certificates:
For vCenter Server 5.1: Select Toggle certificate setting so that the Certificate regeneration enabled displays Yes. For vCenter Server 5.5: Select Yes under Certificate regeneration enabled.
Click Submit.
Reboot the vCenter Server Appliance.
After the vCenter Server Appliance reboots, confirm that the Certificate regeneration enabled option is set to disabled.
Upgrade to vCenter Server Appliance 6.0.
To resolve the issue in a post upgrade vCenter Server Appliance 6.0: