I have (I think) the same problem and for GTA3 and VC. The error says something like "The file is too big for replacement" or something lie that. It is problem with a IMG Tool and it is unrepairable.
Yes, you right it was a little boring and I think that somewhere out there is a script mod for VC that allows you to do a bank robbery any time you want but it was just a repeating a mission.
And then the game is incredibly boring!!! With bunch of cheats around you, it's just not right!
I would be happy if R* make a game without cheats, but most of you wouldn't!