I got this same issue whilst I was trying to do theatre mode in Black Ops 2 - the only other part of a game I can remember as being a must-be-connected-to-the-internet-at-all-times single player mode. I get the feeling that wasn't the first time I had this issue in an identical sort of circumstance, either.
Basically I keep trying to play Contracts mode, and 90% of the time I am forced out of it because of this message (see attached, or https://www.dropbox.com/s/4bsk7vqc9f7c529/2013-02-08%2018.54.04.jpg ).
Now I had thought that it might have had something to do with this device that Comcast installed so my Xbox would actually be able to connect to xbox live at all (because all of my 3 xbox systems simply could not reliably connect to my wireless router-modem) linked here http://support.netgear.com/product/XAV2101v1 , but after I called Netgear they told me that utility wouldn't help, because as we discovered - every light remains green when the disconnects occur, which should mean that it's not getting bored with being single-player-only and going into its own built in sleep mode...which apparently it does have. On the other end of my home though I noticed it sporadically went orange, but when I looked around the time of a disconnect it also seemed green.
So I'm at a loss. Can anyone help? Here's some relevant info:
My ISP: Comcast
My Router: Xfinity Modem/Router combo (which only allows for 5 Wifi connections at once apparently - it still happens when we only have 2-3 devices connected however)
Error Message I keep getting that kicks me out of the game 90% of the time: https://www.dropbox.com/s/4bsk7vqc9f7c529/2013-02-08%2018.54.04.jpg
NetGear device that may or may not have something to do with it: http://support.netgear.com/product/XAV2101v1