It will say unable to download GTA IV at 68 percent. I tried deleting the data and starting over and it won't work. I tried turning off my xbox and turning it back on and it still doesn't work.
Check if you have enough space for it. It's like what? 5 gigs? Try to download again and make sure your internet connection is not being interrupted. Then reset your internet connection and try again. If that didn't do it then I dunno.
Sometimes your xbox 360 can have trouble downloading from xbox live, I've never come accross this before, but it will most likely help if you follow these links:
<http://www.upnp.org/> For activating UPnP
<http://portforward.com/> For opening ports, but be careful which ports you open.