You may have noticed that every once in a while you used the Library Manager and ended up with a corrupt library file -- which doesn't reveal itself until you start pI3 and it crashes at startup.
(a crash at startup could also occur if you had the preview window color set to "image" when pI3 was closed, but that's a different issue)
I've finally figured out what exactly was causing this library corruption: The problem occurs when you delete the first folder of a library using the library manager.
Here's what you can do to avoid the corruption: delete the library folders using the emitter properties dialog (not the library manager), then use the library manager only to add new folders, add emitters, etc.
Of course this will be fixed in 3.0.2. I'm not sure if this problem occurs on the Mac version of pI3 too, but I think it does.