I have a licensed copy... The same situation as with others... I captured all the cities, freed all the heroes, but the checkmark isn't there... even though the garrison requirement is fulfilled... The army in the castle is so large that I can only defend with archers and sorcerers... the rest don't even come out... And there's no end in sight to the raids... and to the mission itself...

Although I have six heroes purchased, I'm currently freeing two mandatory ones, and in the castle, I'm leveling up a new one to level 24 while defending :)