I paperweighted my MG7520 too with the same error code. Unlike you, I did not experience printing issues before the 1403 error code. I just got tired of seeing the update message on the display so I finally gave in and installed the firmware update (version 4.030) and power it off. I only use this printer for color printing because I have a black and white laser printer. Yesterday was the first day I have powered on this printer since the firmware update and like you I received the 1403 and can't do anything with it. I did see somewhere that this can occur it the firmware is corrupted and unfortunately, I can't figure out how to reinstall because it says it is busy. I am upset because I had just replaced all the ink cartridges just before I did the firmware update. Since your last step was the firmware update, I thought it could be related. For me, I'm kicking myself because it was working perfectly before the update.
