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When i upgrade seditio to cotonti i have this error

Where is the problem?

Warning: require_once() [function.require-once]: Unable to access /functions.php in /home/thegame/domains/thegame.lt/public_html/index.php on line 23

Warning: require_once(/functions.php) [function.require-once]: failed to open stream: No such file or directory in /home/thegame/domains/thegame.lt/public_html/index.php on line 23

Fatal error: require_once() [function.require]: Failed opening required '/functions.php' (include_path='.:/usr/local/lib/php') in /home/thegame/domains/thegame.lt/public_html/index.php on line 23