Mojave installation fails: duplicate App Stores, can't sign in with Apple ID (Macbook Pro, Late 2016)

OK, I just spoke with Apple engineering and they gave me a fix for this. It worked for me and it may work for you. You must know how to use Terminal and access hidden directories with Finder in the root of your drive.

First, make SURE that you've backed up the directory /Library/Security/Trust Settings. Copy it on your Desktop or Downloads directory, or wherever you'll be able to access it.

1. Again, back up the user certificate trust settings files described above. Then, remove them with the following commands, entering your administrator password when prompted:

cd "/Library/Security"

sudo ditto -ck "Trust Settings" TrustSettingsBackup.zip

cd "/Library/Security/Trust Settings"

sudo rm *.plist

2. Attempt to sign into the App Store.

This didn't work for me until I restarted at which point I was able to log in and see all of my accumulated updates. If you're not comfortable working at the system level, DON'T do this. If you are, this may fix your problem. It did for me.

Once you're sure that you've got the App Store working, you can delete the TrustSettingsBackup.zip file as well as the backup of the Trust Settings directory.

Let me know how it goes.

I have exactly the same problem with a late-2016 15" MacBook Pro with Touchbar. There are definitely leftovers from the previous App Store installation. While the High Sierra application is gone, the system parts still remain. Here's what I've extracted from system.log in Console. Unfortunately, these files are owned by Root and can't be changed or manipulated by the user, even with Admin privileges.

Sep 25 07:26:13 Rons-MacbookPro-3 App Store[2783]: DEPRECATED USE in libdispatch client: dispatch source activated with no event handler set; set a breakpoint on _dispatch_bug_deprecated to debug

Sep 25 07:26:21 Rons-MacbookPro-3 App Store[2783]: objc[2783]: Class ITNSImage is implemented in both /System/Library/Frameworks/iTunesLibrary.framework/Versions/A/iTunesLibrary (0x7fff86114568) and /System/Library/CoreServices/SetupAssistantPlugins/iTunes.icdplugin/Contents/Ma cOS/iTunes (0x11f5567c8). One of the two will be used. Which one is undefined.

BocaBoy wrote:

1. Again, back up the user certificate trust settings files described above. Then, remove them with the following commands, entering your administrator password when prompted:

cd "/Library/Security"

sudo ditto -ck "Trust Settings" TrustSettingsBackup.zip

cd "/Library/Security/Trust Settings"

sudo rm *.plist

This worked perfectly for me - many thanks for posting!

Yes, this worked for me also, allthough I had to take the extra step of disabling SIP.

Interestingly, the Trust Settings folder was empty before and after deletion. Looks like some kind of bug Apple has seeded with their install of Mojave.

My MacBook Pro started having serious issues after "failed update 10.14."

Mail was the worst hit app, I tried different ways to fix the problem but no success.

Ultimately I did a "clean reinstall" which sorted out everything and computer is now lightning fast.

Worked for me! I had to wait a bit after relaunching the app store for everything to sort out. Thanks!