DLC 7 and 8 are Foundation and Sanctuary so it makes sense that those would be disabled.  However, that should not affect DLC 1-6.  Are you getting this message in Private Matches or Public Matches with your brother?

If your brother tries to play in a public match (without you), can he connect or does he get the same error?  If you try to play in a public match without your brother, do you see this message? 

I apologize for the delay.  I am trying to figure out what may be causing this issue and if it is something to do with a new file on your system or something to do with older files on your brother's system.

Please have your brother verify the integrity of his game cache and see if either of you experience this problem separately.

Thank you for your patience while we work to resolve this for you.

Hi again admiral_basil78,

Have you guys both tried the steps in the link below?

http://shortText.com/GK2rtEQ

I would recommend contacting Activision customer support via phone/chat so they can create a case and document the issue for you. You'll want to let them know what you have already tried, as well.

Please log into the support site for contact options:

http://support.activision.com