giusto, me ne ero dimenticato...
ho trovato questo:
[Tue Feb 26 14:13:21 2008] [error] [client 124.183.109.189] File does not exist: /home/xxx/public_html/forum/500.shtml
[Tue Feb 26 14:13:21 2008] [error] [client 124.183.109.189] Premature end of script headers: /home/xxx/public_html/forum/index.php
il secondo mi preoccupa di piu'!!