Microsoft Connect is the Microsoft beta site. If you got an invite code then you were invited to a beta and since you didn't reply in time you're invitation has expired. At some point you must have applied to be a beta tester for something or you wouldn't have got an invite. They just don't send them out if you don't apply.
They moved from beta.microsoft.com the old beta site just before the Vista beta started. They have some pretty good stuff going on there.