App Store updates do not install

Do the following:

From within App Store

Sign out

Close App Store app

Launch the Music App

Sign out

Sign in

Close Music App

Launch App Store

Sign in

Update apps

I followed your instructions however it appears that when I attempt to sign-in to the App Store it isn't working. I get no acknowledgement that I've signed in nor does the "Signin" action (under STORE) change from "Signin" to "Signout" or does "Signin" grey-out. I know that I am using the correct password because when I enter a bogus password...it let's me know. Does this make sense?
Update: While working on another app I use (Weather Dock) their website (Veros) linked me to their entry in the App Store. There I found "UPDATE" associated with the app which I selected and lo & behold...the exact same problem trying to sign into the App Store& no update is performed.

Try this:

1. Create a new user account (I think it should be an administrator.)
2. Log out from all current accounts and log into that new account. Do NOT set up an Apple ID. Do not enable Siri or Touch ID etc.
3. From the new account's Terminal, run this command:

   sudo softwareupdate --clear-catalog

4. Restart.
5. Log into that new account.
6. Open the App Store, and try updating. When asked, provide your Apple ID (but only in the App Store!)

I had the same issue since Developer Preview 1, and this worked for me.

I'm still not sure if my existing, primary user account can apply app updates now or not.