Connection to ArenaNet suddenly gone?!?

I've recently taken up GW again after having been away for several years. The game has worked fine and I have had no issues at all but suddenly about 15 minutes ago, the game suddenly stalled right near the end of the Tahnnakei Temple mission and now I can't connect.

I can reach the character selelection screen but then when I try to go further whether it is with a PVP or a PVE character, nothing happens. The bar just stays at 0% for a while and then a message comes up that says: "Guild Wars was unable to connect to the game server due to a network error. This may be caused by internet routing issues or a server network failure."

I haven't had any problems with the internet otherwise and I find it hard to believe that my router has suddenly changed it's settings by itself.

What to do?

Hmm, I just deactivated Windows Firewall and then activated it again. Now it's working fine again. Weird.

I had the same problem and it gave me the same reason as you when trying to log in. I reset my modem, PC and router and nothing worked.
I just kept on trying to log back in and eventually got back on. Must have been a server issue.