That's very weird. We have not had reports of anything like that happening before. It sounds like there's a problem with the savegame file(s) and/or their location. Follow the instructions in this post for locating the savegame files, but delete them instead of backing them up. You might also want to search your computer to make sure that there aren't any other Plant Tycoon files in "rogue" locations and delete them, as well. If that doesn't help, you may need to reinstall the game.