I had a lot of cook failures in the past. I already have a personal FAQ to help myself to deal with these errors.
But this time I have no clue about this error. I can’t pack my game because the cook is failing. The logs doesn’t show anything I can understand. Anyone can help me?
The attached file contains the output log.link text
The only “error” that appears in the log is an “Unable to create a widget outered to a null world”. I have no idea what it means (Google doesn’t have any answer too).
It was not exactly that, but it was a similar situation: the error was in my C++ code. I don’t know exactly where, but I checked all my calls to the CreateWidget function with an “if (World)” and it’s working now. 
Yeah, I read it was something about creating the widgets when there was no controller. I would make sure you are creating all your widgets on your controller or make sure the controller exists. If you are just checking now and it fails, your widget probably won’t be created <3