Help, I can't comment on pages

Hi.

My site is http://www.skakistiko.com/ and I installed the theme StudioPress_Red 1.0.

I can write comments on posts but I can not write on pages.
True, I edited header.php, but even when i returned to default, the problem remains.

The same problem appears in a few other themes. I deactived all the plugins, no solution.

Is there a way to resolve it?

Thanks in advance.