That's a good question. This sounds potentially very complicated, so a quick fix seems unlikely.So the issue is with the old save... now what can be done?
And at the moment we don't really have anyone active who could give it the attention it probably deserves.
In other words: We could be stuck between a rock and a hard place here.
@Grey Roger: If you use the savegame from post #5 above, are you able to replicate this error?