Trying to add an ESX 3.5 server to vCenter 4.x throws the error: “The license server 27000@172.x.x.x for vCenter Server somevCenterName does not include vCenter agent for ESX Server. Upgrade the licenses on the license server.”

Ran into common problem that other administrators have probably come across the other day when I was migrating some old ESX 3.5 hosts to a new vCenter where I get the following error:

The license server 27000@172.x.x.x for vCenter Server somevCenterName does not include vCenter agent for ESX Server. Upgrade the licenses on the license server.

There’s actually a public VMware KB available here:

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1013263

As per the instructions from the KB, you need to completely remove the host from your VirtualCenter:

… before you add it to your vCenter server.