Core issue
If the spoke router is configured with the dynamic IP address, the cached nonbroadcast, multiaccess (NBMA) with the Next Hop Resolution Protocol (NHRP) address on the hub does not match to a new dynamic NBMA address with the NHRP address. If this happens, the %NHRP-3-PAKREPLY: Receive Registration Reply packet with error - unique address registered already(14) error message appears on the spoke router.
Resolution
In order to resolve this issue, configure the ip nhrp registration no-unique command on the spoke router.
If the unique flag is set in the NHRP registration request packet, a Next Hop Server (NHS) must reject any registration attempts for the same private address that uses a different NBMA address. If a client receives a new IP address, for example on Dynamic Host Configuration Protocol (DHCP), and tries to register before the cache entry on the NHS times out, the NHS must reject it.
If you configure the ip nhrp registration no-unique command, the unique flag is not set, and the NHS can override the old registration information.
This command is useful in an environment where client IP addresses can change frequently such as a dial environment.