Apple never chimes in it seems when there are issues with competitors, especially Windows.
Anyway, I'm an avid user of Windows 8 and everytime there is an update, it seems to corrupt the iCloud Control Panel.
What I do each and every time, including after installing the new Windows 8.1 update, is this:
1. Close out Outlook,
2. Go to Control Panel and uninstall iCloud,
3. Restart Computer,
4. When computer restarts, open Outlook. Go to File, Options, Add Ins and make sure the "iCloud Outlook Add-in" doesn't appear anywhere. Now click OK, and click Calendars. Under your calendars, you will still see iCloud but if you select it, nothing will happen especially the error message everyone is speaking of.
5. Close Outlook,
6. Download the latest iCloud Control Panel (as of today, it's 3.0),
7. Follow all the prompts.
8. Sign in to iCloud and go through the set-up. Make sure to select ALL when downloading from the Cloud, and NOT Some!
9. Open Outlook.
10. All your contacts and appointments should magically appear.
This simple 5 minute fix should work for everyone.
Hope this helps!