Both my wife and I are having the identical problem on our PC’s running Office 2016 (I have Windows 8.1; she has Windows 10). I believe this problem was caused by an Office update. Both computers have an iCloud account tied to them. When we attempt to change a contact in Outlook, we are greeted with a message stating “Your changes cannot be saved because you do not have permission to modify some or all of the items in this folder. Do you want to save a copy of this item in the default folder for this item?
On the Apple forums, there are a 128 people with the same problem, all starting about 5 days ago. Several people describe contacting Microsoft tech support, which points the finger at Apple and Apple pointing their finger at Microsoft. Many people agree this occurred after a recent MS Office update. A workaround consists of changing the contact on the iPhone which then syncs the change with Outlook.