I found the following in the readme of v3.5.2 of vBSEO;

Quote Originally Posted by vBSEO
Lighttpd Web Server
In step C of the installation process defined:

Instead of uploading the .htaccess file, open your Lighttpd Control Panel and enter the rules defined in the lighttpd_rewrite.txt file included within the 'htaccess' folder of the installation package (replace "/forums/" with your vBulletin folder name).
Hope it helps.

JGM.