To reproduce, do the following:
From the start menu you go to campaigns->resume from last save. You're presented with an expandable list of campaigns. Each campaign has a nested list of "sessions", in which the various saved games are shown. If you delete all of the save files in a given session, the entry for that session isn't removed even though it's empty. Then if you try to highlight/expand another session, the game throws some kind of out of range exception. See the attached screenshot of the stack trace.
Hope that helps!
