Bug

Very cool game concept... Some strategy and different units makes game fun HOWEVER sadly for me I cant use different units I can use it level 1 first unit!!!! I have a bug where every time I click on an upgrade my game freezes. I cant do anything except close and restart the app. How far do you think you can get in the game with just level 1 units? I have no idea but it is boring and Im frankly not gonna keep trying :/ Patch bug

Luke1234567895675433366 about 2012 Zombies vs Aliens, v1.1.2