I opened an unfinished level file (originally created with an older version) in the editor, finished and saved it, and edited my GemLems levels.nxmi to refer to it. The level loads fine in the editor and playtest mode, but trying to open it in NL causes a crash. I've screenshotted the error message, and attached the level file just in case that helps to pinpoint the problem.
[EDIT: Since I am no longer experiencing this problem, I've removed the level file.]