I've configured Exchange ActiveSync, so why are users getting a 86000C0A error when trying to synchronize?

A: The 86000C0A error is caused by incorrect permissions on the user object. Typically it's because the user object isn't inheriting permissions from the parent containers that are required for Exchange ActiveSync. The solution is as follows:

1. Start the Active Directory Users and Computers management tool.
2. From the View menu, select Advanced Features.
3. Navigate to the user, right-click the user, and select Properties.
4. Select the Security tab (if you don't see Security, the Advanced Features menu item isn't enabled from step 2).
5. Click the Advanced button on the Security tab.
6. Ensure that the option Include inheritable permissions from this object's parent is selected, or, for Windows Server 2012, press the Enable Inheritance button.
   
   Advanced Security Settings with Enable Inheritance Button
7. Click OK to all dialog boxes.

Wait for Active Directory (AD) replication to complete, then resynchronize the phone.