[core:error] End of script output before headers

Hi everybody!

On version 3.8.3 suddenly following situation happened:

[Fri May 27 20:28:03.247841 2016] [fcgid:warn] pid 90115:tid 139849971345152Connection reset by peer: [client 2.234.xxx.xxx:59442] mod_fcgid: error reading data from FastCGI server, referer: http://mydomain/gestione/htdocs/comm/propal.php?id=25&action=editline&lineid=171
[Fri May 27 20:28:03.247923 2016] [core:error] [pid 90115:tid 139849971345152] [client 2.234.xxx.xxx:59442] End of script output before headers: propal.php, referer: http://mydomain/gestione/htdocs/comm/propal.php?id=25&action=editline&lineid=171

Errors like these appear within propal, facture, … every time I try to add, modify, delete lines of these kind of objects. Nevertheless the DataBase commits happen successfully, isn’t it strange!?

The output on the browser is:

Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator at webmaster@mydomain to inform them of the time this error occurred, and the actions you performed just before this error.
More information about this error may be available in the server error log.

Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.

My ISP assures that no changes/updates/upgrades were made.

At the moment no idea how to solve that.

When error 500 occurs, the only solution to diagnose is to get information stored into apache log file just aftee error occurs.

Yes, right, the Apache error log is at the Beginning of my first post:

Fri May 27 20:28:03.247841 2016] [fcgid:warn] pid 90115:tid 139849971345152Connection reset by peer: [client 2.234.xxx.xxx:59442] mod_fcgid: error reading data from FastCGI server, referer: http://mydomain/gestione/htdocs/comm/propal.php?id=25&action=editline&lineid=171
[Fri May 27 20:28:03.247923 2016] [core:error] [pid 90115:tid 139849971345152] [client 2.234.xxx.xxx:59442] End of script output before headers: propal.php, referer: http://mydomain/gestione/htdocs/comm/propal.php?id=25&action=editline&lineid=171

Riccardo