I had the same thing, but I managed to get past that.
Rename your GTA San Andreas folder to something like GTA San Andreas2 (doesn't really matter, as long as SOMETHING in the folder's title has changed). The game should now start properly.
However, now I have the next problem: the game loads fine and all, but as soon as I log in, I spawn, game freezes for about 1 second and then the game crashes.
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