+++THESE ARE ONLY TIPS FOR TEST/LEARN LABS+++
You played around with ESXi 5.1 and the evaluation period (60 days) expired. So you got a valid license key for the free ESXi 5.1 Hypervisor and that works fine. But then you realize that you would like to play around with vCenter features like full PowerShell support. You decide to install vCenter as an evaluation for 60 days and want to add the free ESXi 5.1 Hypervisor to your newly created vCenter Datacenter but you get the following error:
The host is licensed with VMware vSphere 5 Hypervisor. The license edition of vCenter Server does not support VMware vSphere 5 Hypervisor.
1.) If you installed vCenter as a VM onto the free ESXi Hypervisor, please keep it up and running (so the SQL Server VM and possibly the AD VM).
2.) Connect/Login to the free ESXi Hypervisor via SSH.
3.) Execute the following bash commands
rm -r /etc/vmware/license.cfg
cp /etc/vmware/.#license.cfg /etc/vmware/license.cfg
Now again, try to add the host to your vCenter Datacenter. You should be able to select a vCenter compatible 60 days evaluation license now.