错误500内部服务器错误 - apache2 - 论坛ipb

I know there are a lots of topic about this error but didn't find a solution yet... I re-installed a new version of php (5.4.9) on linux and of apache (2.0), all build by me.

I installed wordpress and it works perfectly, but when I try to log or open my old forum (invision power board) an error occoured: Error HTTP 500 (Internal Server Error).

The directory of this forum is /forum Permissions of the folder is: 0755 My .htaccess in root is

DirectoryIndex index.php
RewriteEngine On
RewriteRule ^old/(.*)$ /$1 [R=301,L]
RewriteBase /

And my httpd conf directory is

<Directory />
#Options FollowSymLinks
#Options Indexes FollowSymLinks Includes ExecCGI
AllowOverride All
Order allow,deny
Allow from all
</Directory>

Mod rewrite works perfectly with wordpress, the only problem is with this old forum (with many data saved), any solution to fix this problem?