Why can't I play co-op in Saints Row 2 with my friend even though we have the same DLC?

I have the Xbox 360 version of Saints Row 2. I have successfully played co-op with another friend in the past where we both only had the Unkut DLC. A different friend of mine has all 3 DLC packs (Unkut, Corporate Warfare, and Ultor Exposed), and we tried to play co-op last night but we both kept receiving this error, even after I bought the rest of the DLC:

You do not have the same downloadable content as the host

But... I do. We both tried hosting to no avail. Is there any fix for this?

Both redownload all content - it maybe some of it became corrupt.

I've had this personally happen in the past - in the storage area it also had a strange "failed download" or some sort of item stored there. This doesn't need deleting but may help - its left over when a download has failed previously.

Also, just in case once you've downloaded all the content, load the game in normal "single player" mode, just to make sure your save file has updated with all the new content.