Same problem here.
Running snippet was not helping.
from the errorlog
mod_fcgid: stderr: PHP Fatal error: Call to undefined function wpcx_get_wp_generated_thumb() in /home/xxxxxxxxxxxxxxxx/domains/yyyyyyyyyyyyyyyyyy/public_html/wp-content/themes/zzzzzzzzzzzzzzzzzzzzz/404.php on line 18
and line 18 in 404.php looks line this :
$thumb = wpcx_get_wp_generated_thumb("reference");
What to do ?
