Same problem. I found a link on a Microsoft forum that said:
"Close Outlook, Log off iCloud and then Uninstall it.
Reboot computer, Install iCloud again, and Reboot again
Log in to iCloud through the control panel, set it up again and set up the calendar and tasks
Open Outlook and it should work."
I did this and yes it works. HOWEVER, the iCloud photos does not work. There seems to be a resource or permissions conflict with the iCloud photo folder. (There is another thread on this forum about this unresolved problem.) I turned off the iCloud photos. I recommend not turning it on after you reinstall it.
Now the iCloud control panel won't even open for me so I can't trouble shoot it any further. :-(
But the calendar problem has been fixed which is more important to me at this time than the photos. One step forward - one step back.