Stator Vane,
you didn't say whether other machines you or others might have on the same connexion can get through.
Are you able to ping it or tracert it? If so, can you address the IP address directly from the browser? If not, could there be any intermediate proxy that you might have which blocks pprune? I know for a fact that our firm blocks it
Just for fun, you might like trying it with a different browser - I mean Opera or Firefox.
As Conan said, keep on trying!
BOFH