Well it's a simple txt file. And Construct has no problem reading it on startup. But when you submit a new score, the layout will be changed for a few seconds telling you that it was submitted. Then it will go back again to the first layout where it does the exact same thing as on startup. But this time it crashes. Sometimes you can even see that the highscore list was updated again, but you still get an error message.
I also made a simple CAP where it would just download that txt file and when you hit a key it would download it again. There seems to be no problem at all.
I'm still a little puzzled. Well I will try to figure it out later today when I'm in the mood again.