I'm having the exact same problem, usually I have 140ish people on my list, when I logged in yesterday (and today) I have Zero and it's also asking me if I want to allow people to send messages to my mobile device ??? (MSN is on my laptop)
I've sent in a ticket to Microsoft to see whats what but I've a feeling they've screwed something up somewhere as nothing's changed on my machine and by the look of things I'm not the only person with the problem (thankfully)
Anyone with any ideas please let us know