Ok I had a look around for this error:
Error Code: SMPA60
Meaning: Unrecoverable fault - Please restart the game
Its not your fault, its the fault of the person who created the model and didn't update it with mesh deformation.
Here is a direct quote from ZModeler forums:
Fatal Error SMPA60 was confirmed to appear on models with missing objects. You need to keep the same "extra_*" objects and passanger seat dummies as in original vehicle. At least a complete replace of schafter model does not cause SMPA60 error when missing "extras" were added.
Mesh deformation was updated. Exported models should have the same level of visual damage as original models. You should re-export your models to get them updated.
I suggest you back up your original GTA IV models before you replace them with mods.