This problem may occur if the domain controller that held the operations master role (also known as flexible single master operations or FSMO) of RID Master was removed from the domain and restored from backup. If the role of RID Master was forced onto another domain controller as a temporary replacement, when the original RID Master is restored and returned to the domain, it does not replicate with its direct replication partner and does not reclaim the role of RID Master.
Windows 2000 Service Pack 3 and Windows Server 2003 introduced features designed to help avoid the adverse effects of duplicate operations master roles existing in the same forest or domain. Domain controllers perform an initial synchronization at startup on each naming context hosted on a particular domain controller. A domain controller that holds the Schema Master, Domain Naming Master, RID Master, PDC emulator, or the Infrastructure Master role does not assume ownership of the role until it synchronizes with at least one neighbor for each writeable naming context.