From the Haze Offical Forum, Posted by: Ubi_Wuzzi Community Developer
An update is now available on the PSN to correct the difficulties encountered when inviting people into the Co-op campaign. All you have to do is turn on your PS3, launch the game, and accept the update.
After the auto-install, please go into "Select chapters" to continue your campaign. You will then start from the beginning of the last level you reached in the game.
Thank you for your patience