For one reason or another the dl() function is not defined in my build of PHP5.3.0RC2 (Even though, I'm pretty sure that the CGI SAPI is supposed to explicitly register it.)

I'm going to cross post the rest of this from my blog post:
$install->load() would create an instance of install_install and then load that, which eventually got to the get_available_dbms function call which would then call can_load_dll if a particular DBMS extension was not available. Part of that function is a call to dl() to attempt to load a shared object during runtime.

Only problem is that dl() was not defined and thus it would encounter a fatal error. It wasn’t available in the php-cgi binary I built. Additionally, it wouldn’t display this fatal error because the call is made with error suppression. (I.E: @dl(’stuff’); )

/*So, I added this to code
install/index.php to avoid this problem.*/
if(!function_exists('dl'))
{
function dl($ext)

}

So to conclude: phpBB 3.0.4 doesn’t install when dl() is not a defined function.