Try the stdshape.res file. However, there could be many others in the 'settings' folder, the 'cache' folder, and/or the 'skins' folder which could be causing it as well.
None of the files in the Aces High II installation folder should be marked as read-only.
Why not try this. Rename the 'HTC' folder and install the full version of the game. Then copy over what you need from the old 'settings' folder. See if that fixes it.