Perch CMS

The rewrite rule is correct, so there will be something conflicting with it.

Can you confirm that the RewriteRule ^blog/([a-zA-Z0-9-/]+)$ blog/post.php?s=$1 [L] works fine. Check it works when you change it to something else as well like RewriteRule…

I don't have any other suggestions.

Looking at your post Draft preview not working it seems that the rewriting is working but what to do you actually see on the blog preview page? Or do you get a 404?

Thanks for the update. Sorry to say but I won't use (and recommend to clients) any product where I need to edit core files to get it to work.

Yes, it is working fine.

And the other blog rewrite rule is working?

Yes, I've tried it in an incognito window