Hi,
Following that thread, I’m experiencing pretty much the same error by trying to preview a page. I just upgrade WP on 4.4.1 and ACF on 4.4.5 but previous configuration was working fine.
When I try to preview a page, I get a server error 500. I’ve deactived one by one all the other pluggins of my site, and the problems only disappear when I deactivate the ACF.
Thx for your support on that.
