03_serialize_ical.html doesn't write to ical

Got another problem. If I use the above file, the data from the ical file show up in the scheduler, but if I insert a new event and then reload the page, the event is gone. It seems that it doen’t write to the ical file.

Can I also use an ics file instead of ical? How do I do that?

I got the attached file from a previous post, but I don’t know how to fix the problem. Please have a look and tell me what is wrong. I appreciate your help very much.
ical_mirror.zip (1.31 KB)