This is quite strange.
Just so you know. In the future with any plugin that is 1.2.1 or higher, your Book will NOT appear as boxes in layer 3 anymore. There won't be anything in layer 3 unless you put it there. Now your book for any new Age you make will be in the text editor, under Book. And when you export, that is what the Plugin pays attention to, even if you do have something in Layer 3.
Now why putting in a light is causing your Age to crash just does not make any sense at all. I wish I could be more help with this, especially since it seems many others that are knowledgeable are apparently on holiday away from the forum
I'd wait and see if someone else can come up with an answer. If not, reinstall 1.2.1 and continue working until someone does figure this out for you.