Comment 121 for bug 633352

In my case there was no reminder to delete from the Google calendar. It was clean and did not have the event in it for which the undismissable reminder was showing up. I am guessing that the "Server" where the information had "recently changed" is actually in the cashe.sqlit file. So, Lightning was using an un-updated "server", i.e., the cashe.sqlite file, from which to get the reminder information.

But I am certainly glad to hear that you were able to find a much easier fix.