I have two C600's purchased about 8 weeks apart. One will only run 3CX firmware 13.305.238.28.B. It rejects the firmware 13.366.320.41.2 as not compatible. The other C600 installed 13.366.320.41.2 without issue. Before each firmware install and install attempt, I did reset the phone to factory configuration and also installed the latest Fanvil firmware from their website. 220.127.116.11.B-2017-01-10-u Both phones are working fine but the extension with 13.306.238.28.B reports a not supported firmware version on the phones page on the admin console. Any suggestions would be greatly appreciated.