Yes, you need to have the same version to play. Yes, you can have a game in progress and continue playing it after both players upgrade. It is possible that an upgrade fails to work. Long ago I did have it happen but the vast, vast majority of the time the game continues to work just fine. What you can see is some odd sounds or graphics being used temporarily. For instance with this latest upgrade any existing smoke will look funny after upgrade (seems to be using fire textures instead) but