I had same issue. It's caused (for me at least) by game's checksum getting changed for some reason. If you delete your Imperator folder in the my documents and restart the game it should fix it (It also deletes your save games tho if you dont use cloud, might want to back them up first but if the game was started with broken checksum you wont get achievements still until you start a new save with correct chekcsum.) You can check the checksum if you go to multiplayer screen it shows it at the bottom of the page.