When attempting to upgrade Tableau Server, the following error may occur:
Verification of licensing state failed.
An error occurred during installation.
Server must have a valid product key activated to upgrade. If a product key is already activated, make sure the maintenance expiration date has not passed. For steps to obtaining valid product keys for activation, go here https://onlinehelp.tableau.com/current/server/en-us/sug_plan.htm#UpgradeLicense