If you encounter a bug in this game try doing an emergency restart (found in the store). Warning, this will delete ALL progress, except TechBux and purchases made with TechBux. If this doesn't work, try uninstalling and installing the game. Warning, this will remove ALL progress, including TechBux and purchases made with TechBux.
Please report any bugs to support@fun2playgames.com and provide as much detail as possible - this might inlude thing such as the world it happened on, what you were doing when it happened, if you have restarted the game previously.