While typos are the most common issue I see, that doesn't actually stop the game from working or from working correctly. It's just annoying, and difficult to not correct every time I see them.
I would definitely say that errors with switches are the most common game-affecting newbie problems, of those you have listed. In particular, having several pages with NO conditions, putting the switch (or self switch) condition on the wrong page (usually conditioning the page that turns the self switch on BY the self switch), putting it in a conditional branch rather than the conditions panel (which again gives multiple pages without any conditions).
This also includes those who try to make a cutscene by having 10 events, each with their own processing on autorun, using switches to say who should be active at any point in time.