We are also having the same issue. We use Static IP in our network and no matter what ip we give it says Invalid IP address, it is not letting me to enter even DNS or Gateway IP.
Initially phone didn't download firmware from CUCM 8.6 so we did it manually to the same firmware version which CUCM is having it. Phone firmware Version is 9.1.2-SR
By default we received phones with 9.3.2-11 firmware.
Any suggestion would be highly appreciated.
Thanks in advance