Problem:
The 521/524 phones display an "SPCP token rejected" message while registering with a UC520.
Explanation:
The SPCP protocol differs from SCCP based on the "token" which has been added. This registration token ensures that the 521/524 phones register only with the UC520 series routers (and the recent SBCS solutions).
Resolution:
This is usually resolved by:
1. Ensuring that Auto Registration is enabled under "telephony-service".
2. Removing the "mac-address" entry under the specified ephone.
3. Reset the phone.