5년간 잘쓰고 있었는데 갑자기 에러가 뜹니다.

Warning: include_once(./_common.php) [function.include-once]: failed to open stream: No such file or directory in /home/hosting_users/youlife/www/bbs/board.php on line 2

Warning: include_once() [function.include]: Failed opening './_common.php' for inclusion (include_path='.:/usr/local/php/lib/php') in /home/hosting_users/youlife/www/bbs/board.php on line 2

Fatal error: Call to undefined function alert() in /home/hosting_users/youlife/www/bbs/board.php on line 9

루트에 보아도 _common.php, common.php 파일이 다 있습니다.

한번도 문제가 없었는데 갑자기 뜨니 걱정이 크네요