I am having the same issue. I created a repeating event and invited others to it. It won't let me edit it, nor delete it. I changed my status to "Decline" and it disappears; however, as soon as I try to exit the event window, everything shows back up and my status reverts to "Accepted." The only two buttons I have access to is "Revert" and "Reply." Both end up with the same results - event still shows up and I am still in an "Accepted" status.
I tried editing the original entry as well as follow-on events (later in the repeating cycle). I cannot edit anything other than my status, which doesn't change in the end.
I am running Mountain Lion 10.8.1 on a 6-core Mac Pro. This issue also occurred within Lion (10.7.x).
It also does the same thing on my iPhone - I decline the event, it disappears, but then pops back up a few seconds later.
I am using an iPhone 4 using iOS 5.1.1
Any ideas on how to delete (or even modify times, dates, locations, etc.)?
Jim