Verify that the correct path and file name is being used when running the "tabadmin activate" command.
On a new Tableau Server, often a second offline file needs to be created and processed. Be sure to only run the activation.tlf file from our website one time. It is machine specific and one-time use only.
Verify the FlexNet Licensing service is running, see Verify Tableau Service
Create a new activation file from manage product keys (offline.tlq). For more information, see Activating Tableau Offline.