Thought I’d take a look into concrete5 to see what is was like, and it’s the first open source PHP project installer I’ve come across in ages that complained about anything other than filesystem permissions. PATH_INFO? Most other projects use different mechanisms/variables to do a similar job I assume…
Anyways, go to the concrete5 install directory and create a .htaccess file there with the following contents:
php_flag display_errors off AcceptPathInfo On
If you don’t suppress PHP errors it won’t work, which I read may be related to an Ajax callback failing because the response is full of errors (the installer isn’t written properly? I’ve no idea…)
I’ve also heard that some hosting providers (like GoDaddy) don’t play well with .htaccess files, which unfortunately if that’s the case you’ll have to get in touch with them!