Well I did have this problem as well. It is because you have the modded cruisers, let me guess, that means that you have police and police2 modded? That can be the cause when calling for noose backup. ELS doesn't work well with modded police and police2. And to add on further, when you call for noose back-up, that really mixes up the game causing it to crash. So, now, just try replacing your vehicles.img with your backup of the Original vehicles.img and run GTAIV, see how that works when you call for backup, then if it does, try modding FBI slots and noose slots only, as I said, it is a risk if you mod police or police2 with ELS installed......it's a common problem by the way......