I’m sorry. It seems the bug was caused by a combination of the site using ACF, and WPML not being fully compatible with it. (According to support staff at WPML)
My solution was duplication the site 2 times. One to remove the errors and WPML, and one to make a translated version.
Thank you for your help.
I have not gotten the same error any more, (The function has_sub_field()) but I still get this error.
Notice: Trying to get property of non-object in /var/www/fru-k.no/wp-includes/post-template.php on line 29
Any clues? (I have attached the entire source code for the page with the error. The error appears on line 142. I don’t think post-template.php has been altered at all. I have compared it with other wordpress sites)
I have also attached the frontend index of the working page.
Thank you for your reply.
It is supposed to be installed, and working. I didn’t do anything to the ACF plugin before the error appeared. All I did was deleting a translated version/copy of the main parent page.
It is supposed to be installed and active: http://d.pr/i/kA9K
The translation of the page “Velkommen” is the one I deleted: http://d.pr/i/oWvW
Would you suggest I reinstall the ACF plugin, or something similar? Or anything else?