I don't know for certain, but I would guess it means you don't have access. Are you on the Server machine, or do you have access to it?
The command you provided has both "/" and "\" but I'm not sure if that is a typo. I assume the ">" is a typo? Certainly check the command first, but if you don't have access, it won't do much good.
I'm on desktop and have an user acct created on online tableau.
yes, that was a typo.
I don't know much about a Tableau Online deployment. Have you successfully installed TabCmd?
There is a note on this page about making sure the version is up to date; might be something else to check. Its difficult to provide any solid answers without knowing more about what you have or have not done. Let us know how we can help--you can also reach out to email@example.com for a direct answer to your original question (hopefully)