Mac App Store not updating your apps with “Please login to the account you purchased with” type errors? The simplest fix seems to be to just delete the app from your Applications folder. Refresh the Purchased page on the Mac App Store and now instead of Update, its button says “Install” (well, on mine it says “Instalar”, so whatever language you’re in.)
Seems to work consistently for me…
[Update: title changed to reflect how a human speaks…]