I had an acount in the past and used it once almost a year ago to test out the multiplayer function of live and played GTA4 online a few times had no hassels, no use of bad language etc or any other indiscrtions.
Never really got into multiplayer to be honest so basically had the console disconnected until I reconnected it the other day, I tried to sign in but forgot the password (and the security question:roll

so created a new account and signed in, all seemed OK and then I loaded up COD4 as my first game which loaded OK, then when I clicked on multiplayer I got a message that said I "couldn't sign into Xbox live with that profile".
Tried GTA4 as I knew this game had worked OK in the past but when I tried to log into multiplayer it said that I needed to log into Xbox live then shortly after this message a small icon in the top right side of the screen came up saying that I was now disconnected from Xbox live (?)
Don't really know whats going on and as for the download from the marketplace, it was episode games from Fable II and downloaded OK.
Hope this gives you a bit more to work with cheers