My site is currently down (just happened right after I got this email 5 mins ago) –
PHP Fatal error: require(): Failed opening required ‘/www/mcohq_219/public/wp-content/themes/generatepress/inc/custom-header.php’ (include_path=’.:/usr/share/php’) in /www/mcohq_219/public/wp-content/themes/generatepress/functions.php on line 668
have you done any customization to the Theme files?
There is no custom-header.php file in the GP theme so this must have been added and the gp functions.php is less then 100 lines long which means this has been modified.
I suggest you try disabling all plugins aside from GPP to see if the error resolves. And then re-enable each plugin one at a time to see where the conflict is coming from.