Our sites have the same problem too. We are using IIS, WordPress 4.6, PHP7.0
Whenever submit click, following error appears,
The xxx.xx.xx.xxx page isn’t working
xxx.xx.xx.xxx is currently unable to handle this request.
HTTP ERROR 500
It appears after the upgrade to WordPress 4.6, I’ve tried to downgrade the WordPress to old version, that works without problem.
