[RuntimeException] 
Could not start session because headers have already been sent. "/home/a/advance/att-nsk.ru/public_html/index.php":2. (0)
/home/a/advance/att-nsk.ru/public_html/bitrix/modules/main/lib/session/session.php:117
#0: Bitrix\Main\Session\Session->start()
	/home/a/advance/att-nsk.ru/public_html/bitrix/modules/main/lib/session/kernelsessionproxy.php:42
#1: Bitrix\Main\Session\KernelSessionProxy->start()
	/home/a/advance/att-nsk.ru/public_html/bitrix/modules/main/include.php:180
#2: require_once(string)
	/home/a/advance/att-nsk.ru/public_html/bitrix/modules/main/include/prolog_before.php:14
#3: require_once(string)
	/home/a/advance/att-nsk.ru/public_html/bitrix/modules/main/include/prolog.php:10
#4: require_once(string)
	/home/a/advance/att-nsk.ru/public_html/bitrix/header.php:1
#5: require(string)
	/home/a/advance/att-nsk.ru/public_html/index.php:3