Sometimes unavailable button "Screenshot"

Good afternoon.
Tell me why when beta.eyeproof.net, in tab Analysis, sometimes unavailable button "Screenshot" when I examine the page of the site, introduced by link?
https://drive.google.com/file/d/0B95yfy8zh0P3bEkzRVFsNHBmeVk/view?usp=sharing
Tell me why when beta.eyeproof.net, in tab Analysis, sometimes unavailable button "Screenshot" when I examine the page of the site, introduced by link?
https://drive.google.com/file/d/0B95yfy8zh0P3bEkzRVFsNHBmeVk/view?usp=sharing