Can't save anyone item on site

Hello
I can't save or save&close anyone item of menu, material or module on site
rusland.yostudio.ru/en/
how can i fix it?

Dear Olga.
Thanks you for using product our.
Please give me your account of administrator via private message.
Anh please what is name module that can't save.
I will check it for you

Thank you
i just updated joomla from 3.4.4 to 3.51 version and problem has solved

Hi Olga.
Thanks your feedback to me again.
you can come back when have other question.
I will support for you