Cannot get VM to register with activation key.

I have an vCenter instance with a single vSphere host.
I have a utility VM set up with virt-who.

It's config file is as follows:

[config]
type=esx
server=10.0.1.251
username=vsphere.local\administrator
encrypted_password=
owner=
env=Library

Looking at the rhsm.log, it looks as if virt-who is doing its work.

That said, every single time I attempt to register with a key (either from a kickstart file, or manually), I get "No activation key was applied successfully."

I don't have Satellite, and from what I understand, it's not necessary. I know of another org who has this setup, and it is working. As far as I can tell, our configurations are identical... but it doesn't work for me.

Help?

Thanks,

Aaron Kulbe