Hmm... This can happen due to either:
- The version of nwjs you've selected is a bit broken and just crashes when it tries to load the binary versions of the js files. This is more prominent in older versions (before version 0.43.3, I believe)of it. A workaround for this (if you can't use newer versions of nwjs) would be to use the Metadata Editor (found under Utilities) and add --no-flush-bytecode in the JavaScript Flags.
- The more likely scenario would be that a file wasn't included in the packages (when it should have been) and the bootstrap would assume that the cache is broken (and thus, close the game). I'd need to take a look at a build of the game to examine it, so please send me a test build so I can diagnose it.