Did you make a clean copy of the game before adding the cars ? i never had any problems with my cars, how about your save game is it a clean save ? meaning that if you have any cars saved in your garage the game will crash

Did you make a clean copy of the game ?
Di you patch your game ?
Do you have xlive installed ?

Im kinda sure that its your save game i uploaded you my save game with no cars in any of the safe house's

http://moe8909.deviantart.com/art/Sg...253A1375995622

make sure that u delete the folder in
C:\Users\YourName\AppData\Local\Rockstar Games

and use xlive

This is the location for the save game
C:\Users\YourName\Documents\Rockstar Games\GTA IV\savegames