I reset my upgrade points on mission 3 when I could unlock the armor eater, bad idea since I lost and got locked out from the zeus and got stuck with cannon, missile and vulcan all powered at 10. Quitting from the menu fixed the problem, though.
I clicked Exit once during a zombie defense hard match, now whenever I try playing it, I get sent back to the town screen without warning after a few seconds into a new zombie defense game...