Incorrect Resource URL warning but menu arrows are present
I'm starting to regret having written this check!

So far, I have found four scenarios that result in this false positive:


Your php.ini has allow_url_fopen set to false.  This should be corrected, since it will subtly break other parts of CiviCRM (e.g. extension download, update checks).
Your site is behind a .htpasswd, and thus needs HTTP authentication to access files.
You're using WordPress, which has some much discussed issues regarding its ability to detect the directory its in when there's a symlink.  Follow the third link ("issues") for a discussion of how to fix this until the WordPress-Civi wizards resolve this once and for all.
Your server's firewall is configured to reject HTTP requests to itself.  I don't know a way to test for this other than to SSH in and run netcat, something like nc -v &lt;my ip address&gt; 80.  You want a connection that's "open" rather than "refused".  Note that using localhost instead of the local IP address in that netcat command may yield a different result.