I find, using NTL, that it works if I set an explicit proxy and not if I access the site directly.
So I tried the suggestion to delete cookies, and it worked direct!!
For one visit only, then of course the cookies were present again so it failed again.
As it's just PPRuNe, and it's not just me, and it's of recent origin (few weeks, couple of months?) then somebody at PPRuNe must have changed something ... be nice if you could change it back again, guys, so that people don't have to fiddle around like this to get your site to work.