They may have their settings set up to only allow certain people to view their space. If your emails not on the list, then your S.O.L.
May also be a firewall blocking the site (which happened to me when MSN Spaces was first released).
Seeing as its getting major updating lately, hopefully M$ will take the time to fix little problems like this with MSN Spaces AND MSN/Window Live Messenger.
And Contact Cards are working in WLM