Ahh, two page events.

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TREASURE CHEST EVENT

Page 1's graphic is a closed treasure chest, while Page 2's graphic is an open one. (Make sure to set the Animation Type to Fixed Graphic)



To explain:

Only one page can be activated at a time, and the page with the highest number has priority.

If you activate the treasure chest the first time, the first page is the only one that meets all the requirements (Actually, it has no requirements at all). In that case, it runs the event lines on that page, then ends the event.

The next time you try to activate it, both pages 1 and 2 meet the preconditions - but only page 2 goes because it's a higher number. I also suggest labeling the switch something you'll remember - you don't want another treasure chest (or other event) to use the same switch (unless you want to deactivate 2 chests at once when one is opened.)