I have one phpBB forum on a shared hosting provider, and i get this error
[phpBB Debug] PHP Warning: in file [ROOT]/includes/auth/CAS/CAS/Client.php on line 905: session_start(): open(/hermes/phpsessions/S/T/-/Z/sess_ST-ZhPr8mYrwe, O_RDWR) failed: No such file or directory (2)
[phpBB Debug] PHP Warning: in file [ROOT]/includes/auth/CAS/CAS/Client.php on line 905: session_start(): Cannot send session cache limiter - headers already sent (output started at [ROOT]/includes/functions.php:3906)
[phpBB Debug] PHP Warning: in file [ROOT]/includes/auth/CAS/CAS/Client.php on line 1614: session_write_close(): open(/hermes/phpsessions/S/T/-/Z/sess_ST-ZhPr8mYrwe, O_RDWR) failed: No such file or directory (2)
[phpBB Debug] PHP Warning: in file [ROOT]/includes/auth/CAS/CAS/Client.php on line 1614: session_write_close(): Failed to write session data (files). Please verify that the current setting of session.save_path is correct (4;/hermes/phpsessions)
[phpBB Debug] PHP Warning: in file [ROOT]/includes/auth/CAS/CAS/Client.php on line 1618: Cannot modify header information - headers already sent by (output started at [ROOT]/includes/functions.php:3906)
the strange thing here, is that happened unexpectedly one day, it used to be working correctly. Also in my private directories i don't have any /hermes.
Make sure that session directory is writable or you can set a path yourself with:
session_save_path
This comment is also useful if you are using above function.