You may be able to use an operation like 'tabadmin licenses' (with possibly the need for '--repair') to have the vendor daemon loaded.
I work with a lot of prospective customers trialing Server so get a fair amount of feedback on their experiences. Every now and then one of them reports something similar. The first thing I asked them to do is restart Tableau Server - Not a very satisfying answer, but I've found that 70-80% of the time, the problem goes away.
It almost seems to me like part of the licensing stack doesn't do what it needs to the first time around, but is fine when you give it another at bat. Give that a whirl along with Robert's suggestion, then try the friendly folks at Technical Support.
This occurs because Tableau command is meant to be used from Tableau Desktop and not Tableau Server. So, in this case, the command should be run from the following directory (provided Tableau Desktop was installed in the default path)
C:\Program Files\Tableau\Tableau 8.0\bin