The iCal file attendees are getting has a few problems.
The event is send out in the ics file as an meeting. So it is required to "send" that event to someone, or like youself. Alternativly you can save that event, this is however more complicated.

I suggest to change it to be send out as an Appointment. Just remove the "ORGANIZER" line for the ics file to get that.

Furthermore, the event description is not transfered correctly to the ics file. In the HTML body part, new lines are still marked with "\n" instead of "<BR>"