Someone else (or was that you?) reported the same problem earlier, though with a different icon.
It may be that the server handling this request has a problem or that there was some sort of temporary internet "hiccup".
If you work at a company/institution that has restrictive IT policies, it's possible that they don't allow access to some domains/sites so this request is being blocked.
And of course, you'll need to make sure that you do have a solid internet connection, since the icons are stored in the cloud, not on your local PC.