From: https://discussions.apple.com/thread/7526752?start=0&tstart=0

Apr 15, 2016 10:05 AM in response to FrostyOfTheNorth
Sweet Mother of God.  After losing all my hair, I finally found a solution from digging around at http://answers.microsoft.com/en-us/office/forum/office_2013_release-outlook/outl ook-2013-keeps-disabling-icloud-add-in/5….
 
The solution:
 
1) Run Outlook AS ADMINISTRATOR.
2) Go to File > Options > Add-ins.
3) Click GO next to COM Add-ins.
4) Select the iCloud Outlook Addin and REMOVE it.
5) Close and restart Outlook AS ADMINISTRATOR.
6) Go back to File > Options > Add-ins.
7) Click GO next the COM Add-ins.
8) Click ADD and find APLZOD32.DLL on your machine.
9) Close and restart Outlook normally (NOT as administrator.)
 
Now my calendar is syncing properly.

Downgrade Office 2016 to Office 2013

From: http://www.slipstick.com/outlook/office-365-office-2016downgrade-rights/

Office 365 Home, Personal, and University subscribers who upgraded to Office 2016 and want to 
revert to Office 2013 are now able to install Office 2013 from their account portal.

From: http://www.slipstick.com/office-365/convert-office-2013-click-run-msi-installation/#comment-188796

Diane Poremsky January 21, 2015 at 9:04 pm | Permalink
A very low % of users (only corporate volume licenses) have access to the MSI version of Office 2013, which 
would leave some 95% of iPad/iPhone users without the ability to use iCloud. I know iCloud works with 
Office2013 C2R because I use it.

http://support.apple.com/kb/HT4864?viewlocale=en_US

IMAP (Incoming Mail Server) information:

  Server name: imap.mail.me.com
  SSL Required: Yes
  Port: 993
  Username: example@me.com (use your @me.com address from your iCloud account)
  Password: Your iCloud password

SMTP (outgoing mail server) information:

  Server name: smtp.mail.me.com
  SSL Required: Yes
  Port: 587
  SMTP Authentication Required: Yes
  Username: example@me.com (use your @me.com address from your iCloud account)
  Password: Your iCloud password

From: http://www.howto-outlook.com/faq/backupaddin.htm

Make sure the Outlook Backup Add-in is listed and selected as an active add-in:
Outlook 2003 and previous 
Tools-> Options…-> tab Other-> button Advanced Options…-> button COM Add-Ins
Outlook 2007 
Tools-> Trust Center…-> Add-ins
Outlook 2010 
File-> Options-> Add-Ins 
  
If it is not listed, press the Add… or Go-> Add… button and browse to the following location:
32-bit version of Windows 
C:\Program Files\Microsoft Office\OFFICE##\ADDINS\outbak.dll
64-bit version of Windows 
C:\Program Files (x86)\Microsoft Office\OFFICE##\ADDINS\outbak.dll 

From: http://www.msoutlook.info/question/421

Key: HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Addins\Microsoft.OutlookBackup.1 
Value name: RequireShutdownNotification 
Value type: REG_DWORD 
Value: 1

From: http://www.codetwo.com/kb/icloud-outlook-synchronization-diagnostics/

Use Scanpst to repair your Outlook data files as per these guidelines: www.codetwo.com/kb/211 
(NOTE: you may have to perform the repair a couple of times until Scanpst find no errors in your Outlook data files)
IF, DESPITE APPLYING THE ABOVE SOLUTIONS, THE PROBLEM PERSISTS, BEGIN THE BELOW DIAGNOSTIC PROCEDURE.