Changing affinity:
1) Run your GTA:Sa singleplayer
2) Open task manager but let the game run
3) Choose applications tab
4) Right click on GTA:San Andreas
5) Left click on go to process
6) Computer will automatically find the gta_sa.exe process
7) Right click on the process
8) Choose Set Affinity
9) If a box opens, you check only the box in front of CPU 0
10) Done.
It's the place man not your SA:MP or GTA, this problem happens to me like 1 month ago. Try tun run your SA:MP as an administrator.
And uhh, it is highly unlikely that it is a privilege problem.