After finishing developing my site, I updated WordPress to version 3.8. Everything works, but for some reason, an editor cannot click on the Preview
button in the back end. Visiting the link http://www.domain.com/?p=160&preview=true
manually works though!
I don’t know if this is really a version 3.8 problem, as I did not test this before.
luke reports that this issue has been resolved in the comments of the original question: