I wonder if anyone has any ideas.

I have a Toshiba laptop running Windows XP sp2 with an inbuilt
wireless capability.

To connect to 90% of wireless networks, I switch it on, select the
network, and away we go.

One of the train operators in the UK offers wireless on board -
unsecured. Everyone in the coach uses it ok, I get connected, get an
IP address, can resolve DNS names but cannot ping or do anything more
with the outside World.

What always needs to happen is that the operator needs to "manually
authenticate the laptop to the server" - their words.

Once this is done, all is fine but it would be good to know why.

Any ideas?