Well, I started by uninstalling the AOTK3 files, then I uninstalled the OP 4.0+ files, and reinstalled them. At this point, after accessing the Single Player side, the game crashed to desktop as soon as I clicked on the button to select a new campaign. So, I uninstalled OP 4.0+, then uninstalled OP completely, deleted the files left behind, did a restart, and reinstalled everything from scratch. The result was that the game crashed straight to desktop at exactly the same place as it had before.