hi.
my opinion for u is that ur gta san Andreas shows this problem because while installing it some files are shown corrupted especially/mostly two files
1: ...models/(gta_int.img or gta 3.img or both)
2: ...streams/beats.
and the main and only cause of this problem is that ur cd/dvd is scratched..!!
So i recommend u that u buy a new cd without any scratch.
good luck