Some of my calendar events disappeared- any ideas?

Today a number of my calendar events just disappeared, others were still left. All calendars are still checked. I tried several times restoring through Time Machine through the Library. They came back once, but they disappeared again. In subsequent attempts the missing events didn't even show up even though they were there at the time of the back up I was using.

I use an Macbook Pro, iphone 4 and iPad. The whole system has worked seamlessly until today when I was trying to enter a new event and this happened.

Unfortunately the events that disappeared also are gone from my computer, my phone and iPad (and iCloud, too.)

I believe this is a glitch in iCal. Is there a way to fix iCal?

Thanks.