Android 4.1.2 was installed on my Samsung Note2 N7100, then I had installed a custom software CM10.2 Android 4.3 and everything went fine. Then I re-installed the official Android 4.1.2. It worked but when I attempt any call it gives me the error “Not registered on network” and the IMEI code changes to a weird new one. Note: when I re-install the custom software everything works properly and the IMEI changes to its original one. What do I have to do to solve this problem? Is it about unlocking something? Please I need help!