I'm getting the exact same message. I've tried every "solution" I've read about online. To no avail.
I can connect to any site on the internet EXCEPT OpenOffice websites. If I click on "get more extensions online" in OpenOffice it won't load the page. I've even added the page that won't load to my trusted websites list.
http://templates.services.openoffice.org/?cid=923508 <---- the url that won't load in Internet Explorer OR Google Chrome.
It used to work perfectly. It seems as though the templates site is down or unavailable for some reason.
GB

OpenOffice 4.1.5 installed and previously working perfectly on Windows 10 HOME 64bit