Outlook calender event error

This is a two part question. A few weeks ago I had sent out a meeting request, now on the day of the meeting I decided to look at who would all be there and as soon as I opened the event an error occurred " Operation failed. The object could not be found." How could I fix this if it happens again? The second part is now that meeting has passed even though I specified to dismiss the reminder once already the meeting reminder still comes up and I can not delete the event off the calendar at all now. Any Ideas to solve this? I have set the reminder to remind me again in two weeks just so that it doesn't pop up on a daily basis.