First of all, have you activated the script every time you start a game or load a savegame? (Click on a town, click on the advisor's picture, click "Show Me How" button.) If not, you should start a new game and always remember to activate the script since the game doesn't work correctly without it.

If you have activated the script, check your towns. There may be "Polybian Era" buildings added to the building lists in Italy. If so, you have to upgrade your MIC (barracks) in every town one level to get new units.