You can easly check what's happening in the enteire envoirment by enalbing CI logs,
go to config/config.php and edit this:
/*
|--------------------------------------------------------------------------
| Error Logging Threshold
|--------------------------------------------------------------------------
|
| If you have enabled error logging, you can set an error threshold to
| determine what gets logged. Threshold options are:
| You can enable error logging by setting a threshold over zero. The
| threshold determines what gets logged. Threshold options are:
|
| 0 = Disables logging, Error logging TURNED OFF
| 1 = Error Messages (including PHP errors)
| 2 = Debug Messages
| 3 = Informational Messages
| 4 = All Messages
|
| For a live site you'll usually only enable Errors (1) to be logged otherwise
| your log files will fill up very fast.
|
*/
$config['log_threshold'] = 0; //put this to 4
then if you have not yet a /logs folder inside your /application folder, create that and add 775 chmod to that (logs folder only).
UPDATE: You must also chown apache:apache logs in order for apache to be able to write within that folder.
run your application by the browser and check inside your /logs folder the log.php file, it will contain all the application errors.