Honeylamb, hello. Sorry that no one has been able to answer this one yet. It has me foxed too.
I can make only one suggestion, without much confidence that it will help. If you have WA, you might try replacing the meta files, if the fault is there then it may do the trick.
It sounds as if your game has become corrupted. "Fixing/Recovering Saved Game - Saved Game Not in Game Launcher or Corrupted", the sticky above, has lots of suggestions for dealing with corrupted files and includes details of how to replace WA metta files.