vCenter Server 5.5 compatibility with vSphere 4 Hypervisor

[TMachine]

I have recently installed vCenter Server 5.5.0.5201 (With a valid vCenter Standard licence) and I'm in the process of adding Hosts to the vCenter Datacenter. I can successfully connect to the Host but vSphere shows the following error:

"The host is licensed with vSphere 4 Hypervisor. The license edition of vCenter Server does not support vSphere 4 Hypervisor."

Now I found the below compatibility matrix and it clearly shows that vCenter 5.5 is compatible with ESXi all the way back to version 4. I must be missing something, can anyone please clarify the issue.

I know that vSphere hypervisor and ESXi Server is essentially the same but vSphere hypervisor is the free version, so is there a difference that I am unaware of?

[abhilashhb · Accepted solution]

This is happening because you are using a free license key on the 4.1 ESXi.

"The host is licensed with vSphere 4 Hypervisor" means its a free ESXi. You will not be able to manage the free ESXi with vCenter.