After a system update or something else it may happen you get an Exception of your Typo3 Installation. It’s not always the main site but can also could be your „cron“ scripts (cli_dispatch.phpsh)

Fatal error: Uncaught exception 'Exception' with message 'localconf.php is not found!' in ../t3lib/config_default.php:707
Stack trace:
#0 ../typo3/sysext/cms/tslib/index_ts.php(128): require()
#1 ../index.php(84): require('...')
#2 {main} thrown in ../t3lib/config_default.php on line 707

or

Fatal error: Uncaught exception 'Exception' with message 'localconf.php is not found!' in ../t3lib/config_default.php:707
Stack trace:
#0 .../typo3/init.php(206): require()
#1 .../typo3/index.php(63): require('...')
#2 {main} thrown in .../t3lib/config_default.php on line 707

Of course the line numbers could be different 😉
So …. what’s the problem? It so simple that you just forget how you solved it the last time. „Last time? I don’t remember that there was a last time!?“. But you did!
Just check the php.ini and ensure that safe_mode = Off is set. Furthermore check the open_basedir setting. Ensure that (when used at all) all needed directories are set.