One intended vistor in Hyderabad, India, last week reported the same error when trying to access the site from their browser, coinciding with a Host Tracker Domain Lookup Failure alert. As I'm using the free version of the latter, the message I quoted is the total error information available.
The HT error periods are often 30 minutes long (once an error is detected, the tracker tries every few minutes to establish a connection).
I have seen access through my own IP blocked on port 80 shortly after using FTP to upload files. I know the site isn't down because it 's available through a proxy server. After five minutes I have access on port 80 again. Perhaps an over-zealous server IP blocker (I don't use Cloud Flare) is responsible for all or some of these?