The problem is with the folder of windowsapp, The security setting has somehow changed and TrustedInstaller doesn't have sufficient access.
Right click on windowsapp folder (inside program files, if you can't find it go to option and change the setting to view hidden files and folders, just to be sure uncheck the use sharing wizard too.) click on properties, choose security tap, then choose advanced, you can either change the owner to TrustedIsntaller and let it take control of all files and folders and subfolders with inheritance option checked or you can just add TrustedInstaller with the same principle and full control access to users that have access.