I think this is because it exceeds the 20 limit set by the traffic control script.
Because there is a traffic fix used, It means you cannot have vehicles at the safe house.The car pack isn't as high detail as other realistic car packs, I read somewhere that when approaching an image size of 180mb+ with a car pack that the taxi bug sets in.This includes icehancer 1.25, A car pack & working traffic fix, all works well with no errors when playing.
