Seen a few people complaining about importing tactics from the beta into the full game.
The file extensions have changed due to the activation of the Steam Workshop. The .tac files will now no longer show up when imported and what you need to download are the .fmf files.
When you want to share a tactic, you should click the Tactic on the Tactics screen, then click 'Save' - don't use Manage Tactics -> Export. That gives you the preferred .fmf file - and the option to upload to steam workshop, or 'Save' - which saves it in your tactics folder as the fmf file.
If you do download a .tac file then copy the file and place it in your "Tactics" folder in your Sports Interactive folder in your documents. Once you have done that you should be able to see the tactic in the "Archived Tactics" drop down menu on the tactics screen.