Ok, first of all my previous post was a little premature - I was able to get episode 2 to work but then ran into some issues with 3-5, but with a little working at it I finally have all 5 episodes up and running. Here's my story in more detail and I hope it helps (hope you like novels cause this post is loooooong):
First of all - the whole thing was strange for me because I had different solutions dealing with each episode.
For episode 1, I had no complications at all. Ran the launcher and unlocked the game just fine.
For episodes 2 - 5, I was running into this same problem with the script error box. The offending file that would always pop up for me was lib.js, always in Temp/(random string of numbers as folder name)/launcher/include. Since I noticed your offending file is index.js, the following solutions may or may not work for you.
As I said earlier, for episode 2 I looked at the filepath in the error box and navigated to it, making sure hidden files and folders are visible, deleted the file (lib.js for me) and tried again and the launcher worked. However, I think this was merely a fluke for ep 2 because the temp files are cleared every time you close the launcher and recreated in a new folder every time you open it. So I think that for whatever reason, the second time I tried it the launcher just didn't have any stubborn problems with the script.
Because of this I thought I'd be fine for 3-5, however when I tried this for those, every time I reopened the launcher it would create the new folder in Temp with a new lib.js, and have the same problem. Thus I essentially had to turn this into a minigame for myself: My goal was to start the launcher with my Temp folder open, keep hitting F5 to refresh the folder view, and when I saw the new folder created for the launcher (again, it's just a random string of numbers and letters that you should be able to pick out from the other folders), navigate as fast as I could through launcher/include, click on lib.js, and hit shift+delete to kill the file all before the launcher tried to open it. No easy task, as I had to be extremely quick, and it took me a number of tries to do it successfully for each one. I recommend doing a trial run at first to memorize the icon positions so you can do it very fast (I know this sounds ridiculous and you shouldn't have to go to these lengths, but this is the only thing that worked for me).
Now, when I did this for episode 3, the launcher worked for about 15 seconds during which time I was able to put in my unlock code. I don't know if you have an unlock code or not your for game, so this may not help you. After I put in my code the launcher spazzed out again, but it still unlocked the game.
For episodes 4 and 5, deleting lib.js caused a whole bunch of further error windows to pop up involving the other files (probably because of dependencies on lib.js). I just clicked through these error windows and once they stopped I got a simple text entry box over a white background that said "Serial number." Didn't know what that meant but I tried putting in my unlock code, and lo and behold, it still worked!
And for me, anyway, once I actually unlocked the games, I ran into no more errors like this with the launcher when I ran the game. It's only the pre-unlocking launcher that caused the problems. I really hope you understood most of what I said and that this wall of text helps you with your problem. This was a crazy, roundabout and completely annoying workaround, but I'm finally enjoying this great game and it's worth it.