why "permission denied"

baosheng

I encountered a very strange problem today.
My PHP script can't open files whose privilege is 666.

Warning: fopen(./home_page/zzm.txt): failed to open stream: Permission denied in /www/index.php on line 294

Warning: fgets(): supplied argument is not a valid stream resource in /www/index.php on line 295

Warning: fclose(): supplied argument is not a valid stream resource in /www/index.php on line 297

Warning: fopen(./home_page/zzm.txt): failed to open stream: Permission denied in /www/index.php on line 298

Warning: fputs(): supplied argument is not a valid stream resource in /www/index.php on line 299

Warning: fclose(): supplied argument is not a valid stream resource in /www/index.php on line 300

Warning: fopen(./home_page/zzm2.txt): failed to open stream: Permission denied in /www/index.php on line 304

Warning: fputs(): supplied argument is not a valid stream resource in /www/index.php on line 305

Warning: fclose(): supplied argument is not a valid stream resource in /www/index.php on line 306

But their privilege is 666 now:
-rw-rw-rw-  1 root root 4484 May 24 21:38 zzm2.txt
-rw-rw-rw-  1 root root    1 May 21 21:29 zzm.txt


can any one help me?