HTTP ERROR 500 you have any idea how fix such error???? first time on live server and

index.php
some code from ^^^
any comment? // localhost working, BUT live not MAY SYSTEM LIBRARIES NOT ALL UPLOADED WITH FILEZILLA THAT DID????

if ($_SERVER['SERVER_NAME'] == "localhost")
$application_folder = 'F:\htdocs_xampp\CodeIgniter-3.1.9_yyy_com_live\application';
else
$application_folder = '/home/lsepolis123/application';


if ($_SERVER['SERVER_NAME'] == "localhost")
$system_path = 'F:\htdocs_xampp\CodeIgniter-3.1.9_yyy_com_live\system';
else
$system_path = '/home/lsepolis123/system';