I can use ceon addon module perfectly on my localhost with .htaccess copied from configure doc.

However, I ran into trouble when I use the same .htaccess file to my addon domain on lunarpages server. www.myfirstsite.com use another ultimate module for clean url, www.mysecondsite.com point to mysecondsite.myfirstsite.com, and I install seon module on it, both sites Zen Cart are installed in root directory, I can see seon module worked, because I have clean url, however, a page error, can't befound always show up.

I see previous post, one guy modify the .htaccess in parent website to suit the sub domain, I don't think this make sense because I think .htaccess files are organized in diffent directory to manage to rewrite rules for that directory. Can you help? Thanks in advance.