News feed not pulling in Performance Dashboard http 403 errors

Hi,

php5.6 error report is showing:
[05-Nov-2015 16:25:08 UTC] PHP Notice: The data could not be converted to UTF-8. You MUST have either the iconv or mbstring extension installed. Upgrading to PHP 5.x (which includes iconv) is highly recommended. in /srv/users/serverpilot/apps/shop/public/wp-includes/class-simplepie.php on line 1446

nginx.access_log shows:
[05/Nov/2015:16:25:08 +0000] “GET /wp-admin/admin-ajax.php?action=w3tc_widget_latest_news_ajax&_wpnonce=1df0338050 HTTP/1.1” 200

Checked Query monitor & notice a 403 on http requests for https://api.newrelic.com/api/v1/accounts.xml,
http://snag.gy/06QPo.jpg

Thanks in advance,

Phil

https://ww.wp.xz.cn/plugins/w3-total-cache/