Can't get J! 1.5 native SEF working: will SEF Advance work?

I see from the Requirements that native J! 1.5 SEF must be working for SEF Advance to work.

I can't get native SEF to work. The problem occurs as soon as I switch on SEF URLs in the SEO settings (the mod_rewrite switch and Add Suffix... settings work fine). When I switch on SEF URLs my site becomes unavailable except for the home page.

I would like to install SEF Advance 2008 but would appreciate help in getting the native SEF running as it is a requirement. I am using the standard .htaccess file installed by J! 1.5 and have tried commenting/uncommenting out various settings etc.

Another site I operate with the same hosting company is running J! 1.x and OpenSEF and everything works fine.

If someone could give me help with this I would really appreciate it.

Thanks!

Either mod_rewrite or .htaccess overwrite doesn't work then. You must solve it together with your host.
Note that you can use SEF Advance without mod_rewrite in 1.5 but then you will have URLs like:
www.site.com/index.php/section/category/article.html