If you experience this error following a network outage, simply select the Cancel softkey on your telephone as this should restore service. However, keep in mind that the error may appear again. If it does, simply continue to select the Cancel key to utilize your telephone. Once all telephones have been re-registered, the error will cease to occur.
This usually happens when MV_IPTEL server is down or hanged. The phone is not able to get the backup data from the server.
Usually restarting the MV_IPTEL server will resolve the issue permanently.