I suspect you are using the default venue service: http://venues.conferencexp.net/venueservice. I am getting no response from that server today either. Until they get that problem resolved, here are two workarounds:
1. If there's a venue on another service that makes sense for you to use, you can go to Settings Menu->Services and enter/choose the other service, and you should be good to go.
2. If you have the multicast address of your preferred venue, or any other multicast address you can use, you can start the conferenceXP client from a command prompt like this:
"C:\Program Files\Microsoft Research\ConferenceXP\CXPClient\cxpclient.exe" -ip 233.31.135.60 -port 5004
This will both start the client and join a venue in one step. (Note: you'll want to change 233.31.135.60 to a different address -- this is the one we use for our test signals) If you need a multicast address, your network administrator should be able to assign one.
Fred Videon