hook_init() causes login problems
sess_read() should not be used in a module, as that function is passed to session_set_save_handler() from _drupal_bootstrap(), which is the function that is called during Drupal bootstrap.
The purpose of the function is not to read values from the PHP session; if you need to do that, the you can just read the content from $_SESSION[].
To notice that session_start() is called from Drupal during its bootstrap; that means that after a full bootstrap (or any bootstrap that goes past the DRUPAL_BOOTSTRAP_SESSION phase) a session is initialized, and $_SESSION[] can be used.