I applied the procedure to unlock a Samsung Galaxy S3 on a Samsung Galaxy Express I437. It went through smoothly, and but the phone was not unlocked. Instead, it gives me the error message "Phone not allowed MM#6" after I inserted a foreign SIM card. The procedure is reproduced below:
 UMTS  Debug Screen  Phone Control  Network Lock Options Perso SHA256 OFF (after choosing this option, wait about 30 seconds, then go back one step by pressing the Menu button then select Back, now you are in  Network Lock then choose  NW Lock NV Data INITIALLIZ ..... wait for a minute then reboot your phone
Since this didn't work, I tried reverting NW LOCK back to the old setting. Unfortunately, it doesn't work. The unlock screen doesn't come up anymore. And I have no other way to enter an unlock code. Does anyone have any idea how to resolve this issue?