For reasons that are still unknown and under investigation by VMWARE, several of my ESXi 5.0 hosts were not loading the vMotion modules even after multiple reboots.
Run the following two commands from the shell:
vmkload_mod -l | grep migrate
You will get a message saying Module migrate loaded successfully.
Then you need to go into the Advanced settings for the host, then the Migrate section and set Migrate.Enabled to 1.
To be clear this isn’t a permanent fix and VMWARE has advised me against rebooting the problem hosts until they can figure what exactly is going on, but it is allowing me to vMotion virtual machines for the time being.