Reset default ACLs for C:\Program Files\WindowsApps

Resetting permissions works in most cases, but you need SYSTEM permissions to run the command.

The easiest solution is to use PsExec (from Sysinternals).

Open an elevated Command Prompt or PowerShell and run psexec to get a SYSTEM shell.

psexec.exe -s -i cmd

In that Command Prompt, run the reset permission command:

icacls "C:\Program Files\WindowsApps" /reset /t /c /q

Like this to reset permission on this folder:

icacls "C:\Program Files\*" /q /c /t /reset

The things was:

/reset - Replaces ACLs with default inherited ACLs for all matching files.
/t     - Performs the operation on all specified files in the current
         directory and its subdirectories.

I found this answer when searching Google, and it led me to a solution.

ISSUE: Windows apps (such as Mail and Calendar) will not open. Start Menu will not open. Can't right-click taskbar icons.

• Microsoft Store reported issues updating these applications.
• Uninstall/reinstall failed.
• In-place Windows Upgrade ("repair") did not fix the issues.
• Inspecting permissions on the "WindowsApps" directory showed corrupted permissions.
• Error codes 0x80246013, 0x80070005

FIX: Run the reset ACLs command Kattee posted from a Windows Install USB boot disk, using the built-in command prompt for troubleshooting.

1. Follow the instructions on this page to create Windows Installation Media: https://support.microsoft.com/en-us/help/15088/windows-create-installation-media.
2. Boot from the USB/CD
3. When you reach the "Install" button, click "Repair my computer" in the bottom left instead.
4. Select "Troubleshoot"
5. Select "Command Prompt"
6. Locate your system drive
   • The command prompt won't start on your system drive. It will be on "X:\" which is where the USB/CD is mounted
   • You will need to navigate to each drive letter and type "dir" to find the right one, starting with C:
   • Note that this command prompt doesn't use "cd" to change drives (only directories). Simply type the drive letter to switch to that drive (e.g. "D:\")
7. Once you've located the correct drive letter, and switched to it, enter a slightly modified version of Kattee's command, using the drive letter you just found (mine was D:):
   • icacls "D:\Program Files\WindowsApps" /q /c /t /reset
8. Wait for the operation to complete, and check the final output line for any failures.
9. Reboot!

That's what got me working again. Everything is fine after rebooting. No apps even needed to be reinstalled. Everything "just works."