Just a quick guide on one of the ways I was able to resolve my issue with the Windows 8 App Store not being able to update and install addons

For those having trouble following this video:
Step 1: Go to search and type in "Run" to open the run command.
Step 2: In the run command type in "%windir%" then hit enter
Step 3: If the Folder named "AUInstallAgent" is non-existent, go ahead and create the folder.
Step 4: If prompt for admin rights to make folder click allow