Hi Lysemyth, this problem was already reported by another user before and there is a fix for it in the latest beta branch on steam. The root problem is that the AI should have never conquered that landrmark in the first place, but there is also a fix for users like you, where it already went wrong. All you need to do is end your turn after switching to the beta branch (or waiting for the patch to officially dropt) and then end your turn from your save game. Then you should gain access to the archives. 