I noticed this error when trying hide some old shared mailboxes from the global address list, no changes were being synced. Hopefully these steps will help you.
Tom Bullock Death
Click the AttributeValueMustBeUnique link which will take you to a window like this:
Tom has 15 years guiding experience that covers Alaska, Washington, Oregon, and Idaho. He grew up in a fishing family and got his education from friend and guide, Pat Long – former owner of Snake River Guide Service. Tom worked for Clearwater River Company rowing drift boats, guiding for steelhead on the upper and middle Clearwater. Tom moved on from teaching and owned several real estate companies. He first purchased Closser Realty in 1976 and then Closser Bullock in 1979, later changing the name to Coldwell Banker Bullock Realtors. In 1990, Tom became partners with Select. Tom has 15 years guiding experience that covers Alaska, Washington, Oregon, and Idaho. He grew up in a fishing family and got his education from friend and guide, Pat Long – former owner of Snake River Guide Service. Tom worked for Clearwater River Company rowing drift boats, guiding for steelhead on the upper and middle Clearwater.
Press the Details button:
At this point you’re probably thinking you have a duplicate ProxyAddress and its worth checking before carrying on. 90% of the time, this is the case and can be fixed by removing the duplicate in Active Directory. However in my case, it was the OnPremiseSecurityIdentifier that I started focusing on.
Formally trained as a pianist and actor/singer from the age of seven, Tom started professional film work as a film editor on a children's TV comedy series. He has since continued as film & sound editor and post producer on feature films, shorts and trailers in SF and LA., and has performed the same function on many commercials, corporate.
Firstly, you’ll want to find the sourceAnchor (which is also known as the ImmutableID). To find this, click on the “CN=” link under the Export Errors collum (see first screenshot). You should get a window similar to this:
Copy the value for sourceAnchor and make a note of it, you’ll need it later.
Secondly, we need to find the ObjectID of the problematic user. For this, we’ll need to connect to both Office 365 Powershell and Azure AD PowerShell
Office 365:
Azure AD:
To find the object ID:
Copy the ObjectID value and again make a note of it.
Now we will check what the current ImmutableID value is based on the ObjectID we just found:
If all is well, the ImmutableID should match the sourchAnchor value from AD Connect – however, you probably wouldn’t be reading this if that was the case. In my case, the ImmutableID was the users e-mail address, which is incorrect:
Thomas Bullock Bartender
To fix, we need to match the two together (the value for ImmutableID doesn’t need quotes).
To check its worked, run the following command again:
Tom Bullock Fishing Guide
The ImmutableID and sourchAnchor values should now be the same.
Go back to your AD Connect server and run a delta sync:
Tom Bullock Lakewood
The error should have disappeared and the user should be correctly syncing to Office 365.