I can't add any cast in drama. The button isn't available for me. Not only adding but also others things like changing cover images, adding new actors, new drama. This type of things. What's the problem? Others can do it

It's not like I'm doing support for MDL, but maybe you can try different browsers and edit from desktop instead of phone/tablets. If that doesn't work than you have to wait for the staff to look into your problem.