Hello,
To fix this for sure, maybe you instaled some mods or simething before. I saw this problem in the past, so to fix it 100% delete your GTA SA and also MTA and re-install again everything to be clean and you will be able to enter without any problem. When everything it’s clean in the Computer, everything will start to download from 0% without any other problem. Try it and come back and tell us if it’s working. But I’m sure this will fux your problem in download that files, good luck