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I suspect I know why my save files don't work for others. I have a mod installed that allows me to play through all campaigns in version 3.0. I started playing a fan-made campaign called "Year of Fiery Tears." Just in case, I renamed my Campaign.sav file. After that, only the first missions of the vanilla and Armageddon's Blade campaigns became available. I renamed it back, and everything became available again. Therefore, the information about the progress in the vanilla and Armageddon's Blade campaigns is written not only in the CustomCampaign.sav file but also in the Campaign.sav file. It's possible that the game without this mod cannot handle this non-standard information.