Same thing here, now. I managed to launch the game yesterday & got in 3 games of multiplayer before the "error finding a session" thing killed me. Now that they've apparently fixed that, the game locks up my console when trying to launch; sometimes I just get a black screen after the "Dolby" intro, sometimes it gets to the Treyarch loading logo before freezing while attempting to connect to the servers, one time I got as far as the multiplayer menu before it locked up.
I've got the game set to auto-launch multiplayer on startup, so no idea if I can access campaign mode or not as it's not possible to try.
/Also had the same problem with Black Ops 1 locking & freezing starting about two weeks ago. I chalked it up to the game disc being worn out (I can literally see wear marks on the surface), but now I'm starting to wonder. MW3 worked perfectly, but I traded it in when I got the new game; other game discs still work without issue.
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Here is the support link also, always helps to file a ticket with them and check the Knowledge Base too Support for Black Ops 2 Hub