I work on two sites hosted on the same server, using the same CMS configurations and identical .htaccess files in their respective document roots. One site is letting me use the CMS's clean-url mode, and the other isn't. Site #2 functions fine in ?=messy-url mode, but when I turn clean urls on in the admin panel, and request a rewritten URL, I get a 404 error served before the CMS sees the request.

I've contacted the server administrator, but he isn't inclined to provide support and the site owners are beholden to this hosting provider.

I have shell access to the Linux-based server, and I can verify that mod_php and mod_rewrite are active, but I don't know what more I can do to troubleshoot this issue. Is there any way to identify directives upstream that may be differentiating the way http requests are handled by the two sites?

Thanks!