This subject applies to following search terms: problem with copying and pasting events in Thunderbird Lightning calendar; can’t paste an event in Thunderbird calendar etc.
You have an event in Thunderbird calendar called Lightning that you want to copy for a new event.
You choose that event from calendar making a single left mouse click on it. Now you copy that event either by shortcut command Ctrl +C or by right mouse click on corresponding option in context menu.
Nothing happens – no event is pasted.
The issue is more strange as all signs points that everything should work, as pertinent choices for copying and pasting in context menus are active, but even though there’s no expected outcome.
As it turned out upon time wasting investigation such problem can freely happen if in addition to sub calendars (like “my work”, “private”, “events”, “birthdays” etc.) inside your Lightning calendar you have also grouped tasks which labels are also shown in left side of Lighting calendar along to other sub calendar labels.
The issue with unsuccessful paste emerges if you have some of your task label marked (active) prior pasting the copied event. Therefore the event not pastes to your calendar!
Thus in order to make an event show in your calendar do first point out a sub calendar by marking a corresponding label with a click on it.
Generally if any sub calendar is chosen (marked), pasted event shows up in the calendar and you can set appropriate sub calendar editing the event details.
In addition, pay attention that the chosen sub calendar checkbox is marked. Otherwise the event also not seen in the calendar.
Of course there may be other reasons for copying and pasting an event doesn't work with corresponding symptoms (like context menu options for copying or pasting are inactive etc.), but I found that my case can be rather rare and therefore quite difficult to figure out what the problem is, even though the cause of the issue itself is rather trivial. Maybe I just managed to save your time. :)