that is just a handy way to check if the fop2 server is running, if php is not allowed to perform http socket connections (there are some settings that might prevent those), then it will fail, but it won't prevent anything from working really. Check if you have allow_url_fopen in php.ini, also be sure selinux is configured to allow socket connections from php. Anyways, as I said before, that message does not prevent either the manager or fop2 itself from working.
Best regards,