Hello,
First of all, I want to say that I have checked all the related problems but they were totally useless for my situation.
This problem occurs when I try to log in, register, post a question and a comment.
There was a virus in my html files, including q2a files. The virus was adding a code to the top of the html files. Thanks to a application, I managed to delete all the malware codes. But after I deleted them, this problem has started to occur.
In my error_log these problems occur:
PHP Warning: session_start(): Cannot send session cookie - headers already sent by (output started at /*********/index.php:2) in /*******/qa-include/qa-app-users.php on line 149
PHP Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /********index.php:2) in *******/qa-include/qa-app-users.php on line 149
PHP Warning: Cannot modify header information - headers already sent by (output started at /*******/index.php:2) in /*******/qa-include/qa-base.php on line 1365
PHP Warning: Cannot modify header information - headers already sent by (output started at /h*****index.php:2) in /******qa-include/qa-app-users.php on line 1041
[29-Oct-2015 22:57:04 Europe/Helsinki] PHP Warning: Cannot modify header information - headers already sent by (output started at /home/simsdun/public_html/soru-cevap/index.php:2) in ******/qa-include/qa-page.php on line 360