404 submitting the form

When i Add a New Optin Form, doesnt matter what i do, when i hit publish it goes to a 404 page (/wp-admin/post.php).

I updated to the latest version of the wordpress, and i also hitted save on the permalink structure, i have the maestro theme (changed to Twenty Thirteen and did not worked).

Anyone having the same problem? What can i do?

https://ww.wp.xz.cn/plugins/mailchimp-wp/