Lightning is exporting the wrong calender event , in unreadable formats. Scenario ... I have a message from a user on onmicrosoft.com, i.e. coming from Exchange. So note it has the bug where its using mime/alternative. I hit Events / Export and save as text Try and open in iCalendar iCalandar says unregistered. When I open it in text editor, I get the text only (no event) for a completely different calendar invite.
I don't know what you mean with iCalendar application. Please explain in detail. When using menu "Events and Task > Export..." Lightning will export the selected calendar. Or prompt you to the select the calendar to export if more than one calendar is available. The content of the creates .ics, .csv, or .html file should list all events/tasks from this calendar. There is no relationship to email messages or email message attachments.
There is no functionality to export a single event if that is what you're trying to do (you can only export the whole calendar) - you have requested the same already with bug 1239350. Please don't create duplicate bug reports. If you want to import the exported calendar into another calendar application, you probably want to use ics export format.
@MakemyDay, sorry if I appeared to have created duplicate bugs, bug #1239350 was a request to make the process of exporting simpler (you recently changed the title) And this one because it appeared to be exporting the wrong event. Until your post just now, I didnt' realize that Lightning had no ability to export single events, Note that it is precisely because the Thunderbird team say that installing Lightning is the recommended way around Bug #505024 to view and export ICS attachments sent with Outlook, that there is an expectation that Lightning can be used to export ICS attachments.