There is no attachment.

But you are missing the point I am afraid. Those errors really need to be eradicated first.

Okay, I will still contact the author of this theme with the error messages. If he can not solve it, we will buy another theme.
By default theme “twenty sixteen”  work everything clear. Thank you for all your cooperation. I’ll let you know if they have solved it.

If you seriously take a look at other themes I would say that in our experience. paid-for themes are often the biggest offenders. If interested, we use Genesis here and it works real well with lots of layout options.