Need lightttpd clean urls

Hi,

I have started using drupal on lighttpd for the few days.. My directory set up goes like this .

1./document-root/site
2./document-root/site/subsite1
3./document-root/site/subsite2
I am able to get the clean urls for the above sites using lua scripts. I have no problem on accessing the pages using both apache and lighttpd

But I got another site,like

4./document-root/site/subsite3/subsite3.1

When I click the pages on the subsite3 and subsite3.1 I am getting page not found errors when I use lighttpd. but it works fine with apache2. I need help on this.

Thanks in advance...