Errors when indexing a site: why do errors occur about the absence of indexing parameters and instructions?

Question

Search Engine Optimization

Yandex.webmaster suggests the following:
"The robot was unable to access the robots.txt file the last time it was accessed. Unwanted pages may get into the search due to the lack of indexing parameters and instructions.
Please add the robots.txt file."
In google:

With this:

Answer 1

Google has this, forcibly shove (by pressing the send button) into the "Tool for checking the robots.txt file" and select item 3.