SEO links doesn't work

Hello,

Drupal 6.15
phpBB 3.0.6
phpBB SEO 0.6.2

forums/ is an alias to phpbbforum/

On the forum index page, the links are correctly rewrote, like http://drupal/forums/first-forum/ but :

• This links doesn't work (404 error),
• http://drupal/phpbbforum/first-forum show the index of the forum,
• The native url http://drupal/phpBB3/first-forum works fine.

It's a misconfiguration or a bug ?