So far the only known bug is in Level 5. If you get to the END of level 5 after figuring out the puzzle, and cannot open the big exit door, press Esc to go back to main menu and then just select that level and restart it.
If you get stuck on the puzzle... its so easy i'm not going to help you, you will have to keep trying.
I have noticed that the Start Menu isn't actaully working for some people. You may have to enable permmision, my game creates a folder under "My Documents" and that is needed for the autosave function to work. Please let me know if that folder is getting created or not. Thanks.
In Level 3 (Zombie shooting level) you can get stuck in a few places so stay on the sidewalk near the center. Also the Esc button quits the game instead of going to the start menu.