vSphere 6.0: "The given key was not present in the dictionary" under home-> Administration -> Licensing

I am attempting to assign a license to a ESXi server, but when I go to Home -> Administration -> Licensing, I get the following error:

An internal error occurred in the vSphere Client

Details: The given key was not present in the dictionary

This occurs with vSphere Client 6.0

Occurring on every user who has administrative access.

Any help is appreciated!

Thanks,

Chris