S4 active i537 upgrade gone wrong

[call_me_kweKU]

A friend brought me his Samsung galaxy s4 active AT&T(I537) for me to upgrade for him 3days ago. I downloaded stock firmware I537UCUCNC9 (4.4.2) to upgrade it and after sucessfully going through all the processes using Odin 3.09, the screen failed to load and I got a warning message on the screen saying: "System software not authorized by AT&T has been found on your phone.Please turn off your phone and go to the nearest AT&T store for help." Can someone please tell me what is wrong with the phone and how I can fix this issue. Have to fix it before I get screwed.
Image of phone screen shown below
View attachment 175249View attachment 175249

 

[Rukbat]

The "stock firmware" you flashed isn't. It could be a bad file, it could be a bad download, it could be a bad flash, there's no way to tell (unless the site you got the file from lists the MD5 or SHA1 of the file, and you run the file you downloaded to get its MD5 or SHA1 (there are tons of free programs for that) and they don't match - then the download went bad and if you download it again and get a good download it will probably flash correctly. You might want to check [FIRMWARE] [i537] Stock AT&T Firmware Co… | Samsung Galaxy S 4 Active | XDA Forums for NE3, then update to NH3, which is the latest 4.4.2. (NC9, even the official version, is very buggy - that message could be caused by one of the bugs.)

Or get any of the ROMs there working, then bring the phone to the Samsung rep at a Best Buy and ask if he can flash it to the latest 4.4.2. (You don't want 5.0.1 - that still has the memory leak. 5.1 was the first version to fix that. Not understanding that there's a constant memory leak is what's causing a lot of the complaints about Lollipop.)

 

[call_me_kweKU]

...the initial baseband version of the phone is I537UCUAMF3 (4.2.2). hope I didn't mess up by just going directly with the NC9. Didn't touch the OTA file at all.

 

[TheReub96]

Go to XDA & search for the post about 'OC6 & Keep Root'.