Lot of Php cron error

Hi to all

I am testing the version 20.x of Vtenext.
I have this issue: cron report this list of error, here just some of them, how may I correct?
Thank to all for any help

PHP Notice: Undefined variable: _SESSION in /var/www/html/crm/vtigerversion.php on line 18
PHP Notice: Undefined variable: _SESSION in /var/www/html/crm/vtigerversion.php on line 18
PHP Notice: Only variables should be assigned by reference in /var/www/html/crm/include/database/PearDatabase.php on line 22
PHP Notice: Only variables should be assigned by reference in /var/www/html/crm/include/database/PearDatabase.php on line 23
PHP Notice: Only variables should be assigned by reference in /var/www/html/crm/include/database/PearDatabase.php on line 1229
PHP Notice: Only variables should be assigned by reference in /var/www/html/crm/include/database/PearDatabase.php on line 256
PHP Notice: Undefined index: table_exist in /var/www/html/crm/include/utils/Cache.php on line 31
PHP Notice: Undefined index: show_query in /var/www/html/crm/include/database/PearDatabase.php on line 404
PHP Notice: Undefined index: show_query in /var/www/html/crm/include/database/PearDatabase.php on line 404
PHP Notice: Undefined offset: 0 in /var/www/html/crm/include/utils/Cache/CacheClasses.php on line 60
PHP Notice: Undefined offset: 1 in /var/www/html/crm/include/utils/Cache/CacheClasses.php on line 60
PHP Notice: Undefined offset: 2 in /var/www/html/crm/include/utils/Cache/CacheClasses.php on line 60
PHP Notice: Undefined offset: 3 in /var/www/html/crm/include/utils/Cache/CacheClasses.php on line 60
PHP Notice: Undefined index: installed_modules in /var/www/html/crm/include/utils/Cache.php on line 31
PHP Notice: Undefined index: show_query in /var/www/html/crm/include/database/PearDatabase.php on line 404
PHP Notice: Undefined index: show_query in /var/www/html/crm/include/database/PearDatabase.php on line 404
PHP Notice: Undefined index: show_query in /var/www/html/crm/include/database/PearDatabase.php on line 404
PHP Notice: Only variables should be assigned by reference in /var/www/html/crm/include/database/PearDatabase.php on line 480
PHP Notice: Undefined index: action in /var/www/html/crm/include/utils/utils.php on line 478
PHP Notice: Undefined index: search in /var/www/html/crm/include/utils/utils.php on line 479
PHP Notice: Undefined index: module in /var/www/html/crm/include/utils/utils.php on line 483
PHP Notice: Undefined index: file in /var/www/html/crm/include/utils/utils.php on line 483