Siege counterattacks

I am playing as the Romani and a Macedonian army recently laid siege to Ambrakia which I control. For some reason however I am unable to use my units inside the city to attack the Macedonians, this also happened in Athens a few turns ago but I am sure that I have succeeded in counterattacking with a besieged army before. Could it be because I have a client ruler in those cities?

Yes, client rulers prevent you from sallying. Look for bovi's fixes in the bugreport subforum.