According to the error message, it's the vCenter Server Evaluation which has expired.
But I just now obtained a fresh new key from https://my.vmware.com/group/vmware/evalcenter?p=free-esxi6
It should work right?
And we assign it via vsphere client right? And there shouldnt be any restrictions to add at least a single host.
vCenter Server, and the hosts are licensed separately. With an expired vCenter Server license, most actions are restricted, even for properly licensed ESXi hosts..
Also note that an ESXi host with a free Hypervisor license cannot be added to, and managed by vCenter Server.
So now my only way out is to completely reinstall esxi 6 back again.
But I dont want to format my server 2k16 on which vSphere & vCenter is installed. Can I keep them as is or do I need to remove them and reinstall again?
As I think the license is only for vCenter Server right or is it for host inclusive?
Following is list of licenses type so which one will I require along with the evaluation ones provided by vmware
vmware vsphere 6 hypervisor
vmware vsphere 6 desktop host
vmware vcloud suite 6 standard/ advanced
vmware vsphere 6 foundation
vmware vsphere 6 essentials
vmware vsphere 6 standard
vmware vsphere 6 enterprise
vmware vsphere 6 enterprise plus
As mentioned, vCenter Server, and the ESXi hosts are licensed separately, and each of them either needs a valid license (other than the free Hypervisor), or has to run in evaluation mode (60-days as of installation, no license keys required). The Evaluation Mode offers all the features of vCenter Server Standard, and ESXi Enterprise Plus.
For ESXi it may be sufficient to reinstall a host with the option to preserve the VMFS datastore (on which VMs are stored). For vCenter Server, I'm afraid that uninstalling, and re-installing may not reset the evaluation period. Anyway, why don't you install the vCenter Server Appliance on one of the hosts, rather than installing the Windows based vCenter Server? The Windows version will be retired in the near future anyway.