Comment 115 for bug 633352

I had this problem. Struggled with it for months. Tried to dismiss certain recurring events with no luck. They popped back up and when tried to dismiss I would get that "Item has recently been changed on the server ..." pop-up box. So, I looked into my T-bird Profiles folder (it's usually located on path: C:\Users\{your user name}\Appdata\roaming\Thunderbird\Profiles\{xxxxx}.default) Inside that *.default folder you will find a folder titled "calendar-data". When you open that folder you will see 3 *.sqlite files. These are the databases where your calendar stuff is located. The biggest of these, in my case, was the file titled "cashe.sqlite" You will need to be able to access the data in this file because it contains all of the event data for your lightning calendar.

To access this file I recommend getting the Firefox add-on called, "SQLite Manager". After installation you will be able to open this add-on by clicking on the tools menu in Firefos. Load the cashe.sqlite file and look through all of the data. What I found was what I suspected I would find; the recurring event that I was trying to dismiss had a double entry. In other words, this cashe.sqlite file had somehow gotten corrupted. Don't know how and don't care how. The main thing is the fix. There is an option in SQLite Manager that allows you to delete any item, i.e., event, from the data base. I simply found the double entries and deleted both of them! And, VOILA! When I restarted T-bird and the lightning calendar the unwanted items, i.e., all of the unwanted recurring events, were GONE! from the calendar. Bottom line: it's not a problem with T-bird or with the Lightning add-on. IMHO it has to do with something that causes a corruption of the cashe.sqlite calendar data file. In my case, I believe it happened when I messed up (don't know how) porting calendar data from Win XP to Win 7 ... or something like that. Anyway, I hope this fix works for you. And it should work for any non-dismissable event. Good luck!