I have been getting this error just recently a few weeks ago actually.
It usually happens when i get to the part in Liberty "The Triangle"
And i go to a certain point there (By the LCPD Themed Donut Shop) Then when i'm driving or shooting cops or something and they come rolling in with cars (Bohan Police District Modded) Then after i shoot them with a few rockets i walk a few then it minimizes and says: GTAIV FATAL ERROR: SMPA60 -- Please Restart the Game (Or please reboot your System) This happens to me when i'm in Singleplayer (I haven't tried MP Yet) So most people are getting this from an MP, That may be because you're modded files or whatever are interfearing.
But i'm getting this in Singleplayer, it happens after a few minutes or an hour, of play (Or when it gets overloaded or whatever causes SMPA60) But it sometimes has a different error away from "The Triangle" When i'm selecting a certain car for LCPD:FR and sometimes randomly, The other error was something like this
GTA IV FATAL ERROR: RESC10 -- Please Reboot your System (OR Out of Video Memory) (OR SMPA60)
Sorry about the long post
But i'm sooo mad now i'm tired of rocketing cops and getting RESC10s or SMPA60s