Then would be great to check out logs
application > config > config.php
Set
$config['log_threshold'] = 1;
Try to create an user again and see in application > logs if you got a file with some information to provide us (you will maybe need to set CHMOD 777 to the folder application/logs)
Edit : Can you please provide the link of the system you use ? I assume you have downloaded library/package on Internet and install it ? Is that possible to get a link?
