There's something called content blocker in Safari's preferences and WBF was one of the sites that it had picked to block, this all started with a Safari upgrade a month or so ago but it's fine now after removing WBF from the blocked list.
I have gotten the same message when the server is busy. I reported it. They investigated and server was busy. Several others have on occasion gotten the same message. It happened to me again yesterday. I waited 30 seconds and then tried again with no problems