Hi, thanks for letting me know! I just gave it a test drive, and it still work at my end. Good for me, but doesn't help you. :-/
The line 30 is this one: (line 116 is the exact same)
writtenFile = OpenToWrite( "raw:" + GetDocumentsPath () + "\" + saveDir$ + "\" + activeDoc$)
I can't figure out anything which could go wrong here, if the directory string (as shown in the error message) is legit. The only other instance I could find of "Failed to open file for writing" is this one (an Android app where the dev forgot to checkbox writing permission)
Some stuff can be adjusted in \media\settings.txt and in the file C:\Users\User\AppData\Local\AGKApps\AuthorsPassage\media\authorspassage.json But none of those should have any influence on the ability to save a file. I never touched bytecode.byc, but doubt that it's the culprit.
Do you think you could check if there might be something on your machine that is blocking the writing? I can't really think of anything else, sorry!