The reason is Sameera Reddy who was curious working with Kamal started to share about the technical details and cameras used for filmmaking with outsiders.
Kamal who got irked by this reactions of Sameera Reddy asked her to leave the project and later Pooja Kumar got the offer.
Recently few shooting spot stills of Viswaroopam got leaked on the internet which brought the wrath of Kamal on the technical team members.
When he found out the persons, he just fired them out of the team.
It seems that Viswaroopam will have something that Tamil cinema has not touched so far and that's why Kamal is not allowing anything to leak out.