On the iPhone tap Settings > iCloud
Switch Calendars off then back on then reset the Device.
Hold the On/Off Sleep/Wake button and the Home button down at the same time for at least ten seconds, until the Apple logo appears.
On the Mac open System Preferences > iCloud. Deselect the box next to Calendars, then reselect then restart your Mac.
It seemed to work OK on the iPhone, iPad but then we realized some entries we made on the iPhone weren't going through to the iCal on our MacBook Air.
My wife and I share a single identity for purposes of iCloud and Apple ID. That worked fine using MobileMe and Snow Leopard. Once we figured out how to set up the new iPad (version 1) last year, that stated working too. Then, when we got the iPhone in August, we were able to set it up in a similar way.
When I upgraded my older Mac Pro to Lion and we switched over to iCloud, there were problems, but I think I have manage to fix most of them -- your reply was useful in fixing the iPhone an iPad so they seem to be OK now.
But the iCal on the MacBook Air is still not working correctly.
I used the method you give for reinstalling the calendars on the Air. I get a new populated calendar, but missing any entries entered from the Mac Pro. Here's how it stands now:
1. Entries made on the MacBook Pro will not propagate to the MacBook Air.
2. Entries made on iCloud and all other devices propagate correctly to the Air.
3. Entries can't be made on the MacBook Air -- i.e., nothing shows up when I try to create a new event, but each attempt creates a "New Event" that propagates to iCloud and all other devices -- i.e.
I don't know what to try next.
Just a follow-up for anyone looking for their answer here.
Used Express Lane nd the chat advisor reminded me to try an test user and when I did, the iCal worked fine.
Back in the primary user: Quit iCal, went to Finder, /User > Go > (Option) Library > Preferences and dragged the com.apple.iCal.plist file to the desktop, and re-launched iCal.
Works fine now.