Unfortunately since 1.8 or so I've been getting this on my iPhone 4S as well. The game will either crash immediately on launch, or crash while loading if it somehow makes it to the main menu. I'm not using the free version for what it's worth, I've had the mobile version for a while and it worked fine previously. I can always go to the Dota or Steam version, but just thought I'd report for posterity. If you guys need any more info I'll be happy to help.