Licensing problem adding host to vCenter trial

I am evaluating vmware as a virtualization option in our datacenter. I have ESXi 5.1.0 installed on a host, and I deployed the vCenter trial appliance 5.1.0 on a second server.

When I try and add the ESXi 5.1.0 host to vCenter, I get the following licensing error in vCenter (at the end of the Add a Host wizard):

"The host is licensed with VMware vSphere 5 Hypervisor. The license edition of vCenter Server does not support VMware vSphere 5 Hypervisor."

My vCenter is an evaluation copy - is there a separate license I should be using?