This has happened to a mate of mine. Here's what he did wrong:
A) He had obtained a pirate copy of certain DLC installers

He was using someone else's EA account
C) He was foolish enough to try to login to cerberus using said EA account
the result of the above 3 misnomers somehow managed to 'corrupt' (And I use that term VERY loosely) the base game files.
He fixed this by completely uninstalling the game, Reinstalling it, Running the game, Logging into cerberus, Exiting, Then installing the original DLC packs that he ended up buying, To save himself the stress.