I found a solution for me with the apc_fetch() / API error.
Checkout your apache error log /var/log/apache2/error.log.
See if there is something that says:
PHP Fatal error: Call to undefined function apc_fetch() in /usr/share/php/Cake/
Also, check if you can access the zm API: (Zoneminder API Documentation)
Type this in your Browser after you logged on to your zoneminder:
If you got an http error 500, the api is not working.
So if this is true, check your PHP Version.
In my case, i was running on 5.6, but also got 7.0 installed but not activated.
But all important php modules (like ACPU, APC) where activated in the 7.0 config . (howto install acpu)
To switch to php 7.0 do the following in your shell:
service apache2 restart
After that, the Zoneminder API starts working fine.