I had that message on my Firefox browser earlier today.
Quickest way I've found of getting round the problem is to go into my History and look for the last trace of being on here. I don't know about other browsers but Firefox allows me to open that last trace elsewhere from where the '504. Bad gateway' message appears.
Well, that'll teach me to make it sound like I - yer original non-techie! - knew what I was talking about!
As you do at my age, I woke up about half an hour ago, and because I couldn't get back to sleep, I logged in here, hoping that reading some of the threads would help me drop off. However, I got not the '504. Bad gateway' message but one that read '502. Bad gateway.'the
And it took me AGES to find a previous trace of this site using Firefox that did the trick. So apologies to Punterperson and anyone else who thought my earlier post meant a quick fix to the problem. This morning's experience taught me it does the trick, just maybe not first time. Sorry.