No topic listing above for this Thunderbird Calendar issue. Calendar events disappear completely. I have been scheduling series events using the weekly repeat. Then modifying the few that change. Somewhere the whole series just disappears. Example: PT-Kathleen was input as Monday at 11 to remind 3 day's in advance and repeat for three months. Then I modified several that were scheduled differently. All is good for several weeks then 1 the reminders no longer work. Then the whole series disappears. This has happened for about five of these series and I just put all the stuff back in. But, then that disappears also. Any thoughts things I should setup differently?? tired of redoing things multiple times. Robert Kelly