Errors

I am playing on my phone and i am on the second world and I am wondering why it wont let me upgrade Ive read other reviews and it seems to be a problem on other iPhone 5 users and should be fixed, it makes the less fun because you have these low weak guys and cant upgrade but the enemy has high good troops other than that a great game

Reynolds Family Rocks about 2012 Zombies vs Aliens, v1.1.2