Here’s a great set of steps for these:
http://blog.jocha.se/tech/azure-ad-sync-event-error-6126-and-6127
The short of it is:
- Bring up the Syncronization Service Manager (“Synchronization Service” in Windows search),
- Click on Connectors,
- Click on “Active Directory Domain Services”,
- Click Run in the right pane, choose Full Synchronization, click OK, and wait for completion to be reported (it’s fairly obvious),
- Click Run in the right pane, choose Full Import, click OK, and wait for completion to be reported,
- Click Windows Azure Active Directory,
- and do the same two Runs as for the other line item.