How to debug "cannot connect to server"

[toby]

One of my users cannot connect to the server,
whereas everyone else (or at least many others) can connect just fine.

I got what information I could, including part of the console log:
It seems the relevant messages are:
(host name redacted)

[WEBSOCKET, requested host: xxxxxx.info, host: xxxxxx.info, port: 9100] Failed to achieve ready state after 10000ms. Aborting connection... orb2release.js:8
5/28/13 09:54:31.897 UTC+2 DEBUG: [CONNECTION] [WEBSOCKET, requested host: xxxxxx.info, host: xxxxxx.info, port: 9100] Deactivating... orb2release.js:8
5/28/13 09:54:31.912 UTC+2 WARN: [CONNECTION_MANAGER] Connection failed for [WEBSOCKET, requested host: xxxxxx.info, host: xxxxxx.info, port: 9100]. Status: [Client closed connection before READY state was achieved.] orb2release.js:8

Then pretty much the same thing for the HTTP connection,
and then it gave up.

I asked the user to ping the server, which they were able to do successfully.

They are using Windows XP (Win NT 5.1)
Might there be something important missing ?

At that point, I was out of ideas, does anyone else have one?

[toby]

Someone else had a similar problem,
and connected successfully from a different computer.

The one that failed was "at work", the one that succeeded, "at home".

Probably his company has a firewall of some kind which blocks the connection.

Is there anyway to detect such a thing so that an informative message
can be displayed?