[Help]Blank page on production server

[eluser]minoh[/eluser]
[quote author="mattpointblank" date="1268861811"]Make sure your /logs/ and /cache/ directories have write permissions (try 755 or 777).[/quote]

i changed permissions but no success, now i get 500 Internal Server Error and by checking apache errors i found that error log:

suexec policy violation: see suexec log for more details
Premature end of script headers: index.php