I have the same problem: AH1086T1091.EXE quits at Mindanao and exits without finishing the upgrade. I'm left with a partial upgrade (aceshigh.exe reports 1.09 patch 1, but I don't have any of the new sound files). I tried going back to a 1.081 full install and then going 108T1084, 1085T1086, and then 1086T1091, but that didn't change anything. Neither did downloading mindanao.exe. Special circumstances: I don't install AH to its default directory, I put it in D:\AcesHigh.
Will anything short of a wipe and full install fix this? Thanks.
Edit: My fix was easy: when the MA was reset a few minutes ago, and mindanao.res was autodownloaded, I ran AH1086T1091.exe again and this time it worked all the way through.
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