We have 150 phones,only 11 of them registered correctly and the rest give me the above error. Registration rejected:Security Error.
The phone load is currently SCCP42.8-5-2SR1S.
We faced the same problem as well.
CUCM, CAPF and CTL service was running which we turned off. After deleting the Phones when i tried to re-register the phones they started to give me this error. "Registeration Rejected : Security Error" . We also switched the tftp from Publisher to a subscriber server.
Solution : We manually added each phone to the system since they were few phones. You can Use BAT to add the phones if you too many phone having the same problem.
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