New information: I put the error_reporting(E_ALL), and ini_set('display_errors', 1) lines to the index.php. I got some errors:
A PHP Error was encountered
Severity: Notice
Message: Only variable references should be returned by reference
Filename: core/Common.php
Line Number: 257
Fatal error: Uncaught Error: Call to undefined function mysql_connect() in /var/www/html/szig/ci/database/drivers/mysql/mysql_driver.php:73 Stack trace: #0 /var/www/html/szig/ci/database/DB_driver.php(115): CI_DB_mysql_driver->db_connect() #1 /var/www/html/szig/ci/database/DB.php(148): CI_DB_driver->initialize() #2 /var/www/html/szig/ci/core/Loader.php(346): DB(Array, NULL) #3 /var/www/html/szig/ci/core/Loader.php(1171): CI_Loader->database() #4 /var/www/html/szig/ci/core/Loader.php(152): CI_Loader->_ci_autoloader() #5 /var/www/html/szig/ci/core/Controller.php(51): CI_Loader->initialize() #6 /var/www/html/szig/application/core/SZIG_Controller.php(12): CI_Controller->__construct() #7 /var/www/html/szig/application/controllers/main.php(7): SZIG_Controller->__construct() #8 /var/www/html/szig/ci/core/CodeIgniter.php(308): Main->__construct() #9 /var/www/html/szig/public_html/index.php(251): require_once('/var/www/html/s...') #10 {main} thrown in /var/www/html/szig/ci/database/drivers/mysql/mysql_driver.php on line 73
So... this is a database error, because the programmer used obsolote function?
(Anyway sorry for the stupid questions, I am newbie in CodeIgniter...)
