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Hey! same problem here but, by accident, discovered that the problem was the Lilypad wasn't restarting when the compiler was trying to upload the code. Here's the trick, when the loading bar hits 100% press the 'reset' button on either Arduino UNO or Lilypad, both should restart the LilyPad.Some avrdude errors may appear on the log but should successfully upload the program, takes a little time to hit in the right time, but just try it until you get this "error"(image) it means it had problems while uploading the program, but it works! Ps. After some time doing this 'trick' now the Lilypad restarts by itself (I don't know why) and uploads the program still showing this error
How to make an Origami Valentines Pop - Up Heart Box!