Most importantly it never is or was the matter of encryption/security or SSL/TLS protocol.
You can check this by visiting http://gridnet.org (without the httpS prefix).
The server is configured to redirect you to the encrypted website if you chose to use pure HTTP protocol.

Now. There might be a 'WWW' A record DNS record missing from the DNS server (we've switched the provider in recent days, we'll look into this ASAP)

UPDATE: the issue had to do with the 'WWW' prefix being not recognized by the server.