Do you have DLC installed ?
Did you delete them and try again to play ?
I have a friend who had the same problem. He deleted the DLC, loaded his game, played for awhile, saved his game, then downloaded again the DLC, and it worked.
it was on Xbox 360.
Tried deleting DLC and re-downloading, didn't work.
I will never forget you, CBot. You will always be my one true love.