I looked at what might have changed in the SKP since the SKB was saved. The SKP has a few things corrupted in it that make it not possible to recover anything. Two of the corrupt things are materials, named Kadinsky_cover.jpg and LeavesDead0045_1_S.jpg. I don’t see either of those in the SKB file.
Were those materials that belonged to something you have only just imported? If so, what was it that you imported?