500 error with Laravel 5 in subfolder on shared hosting

I'm embarrassed to ask this but none of the other questions have answers that work for me. I am using shared hosting, without access to the root (i.e. all Laravel's files go in the public folder). I know this is unadvisable, but I have no choice in the matter.

I also need to store the app in a subfolder. So I have uploaded everything to htdocs/new. But when I go to

http://ift.tt/1SAb8A9

I get a 500 internal server error. My .htaccess file is unchanged:

<IfModule mod_rewrite.c>
    <IfModule mod_negotiation.c>
        Options -MultiViews
    </IfModule>

    RewriteEngine On

    # Redirect Trailing Slashes If Not A Folder...
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule ^(.*)/$ /$1 [L,R=301]

    # Handle Front Controller...
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteRule ^ index.php [L]
</IfModule>

via Chebli Mohamed