Well, I know I haven't found a cure, but I think Iknow the cause. I was able to do almost the entire game while saving in combat. The bug didn't show untill Marcus died. I wrote him off and saved anyhow.
Later Casedy died, saved anyhow and same issue.
Did a little more testing and I only get the error if I save in combat after loosing a teammate.
Anybody care to verify?