Internal Server Error is registered in browser, in apache error log file I can only see the following warn thrown in same time:
[warn] mod_fcgid: process XXXXX graceful kill fail, sending SIGKILL
Are these two errors related each other?
This seems to be a related problem, with some suggestions on how to solve it: mod_fcgi in virtualmin: graceful kill fail, sending SIGKILL?
I found an answer on my question, the following error is also presented in the apache error log file:
mod_fcgid: read data timeout in 45 seconds Premature end of script headers: index.php
This comes from the fast cgi configuration, I increased the IOTimeout value in /etc/httpd/conf.d/fcgid.conf
FcgidIOTimeout 45 to FcgidIOTimeout 300