The new Notifications Center in Mountain Lion is a pale, pale imitation of good ol' Growl. But after upgrading OSX, the App Store refused to update Growl. Upon clicking the "update" button, the store kept complaining:
"You have updates available for other accounts. To update this application, sign in to the account you used to purchase it."
Don't believe it. At least, don't assume it's returning a correct error message for your situation. While some people do purchase software under multiple accounts, this wasn't the case here.
The actual complication:
The App Store doesn't know how to cope with a previous Growl install — even one purchased through the store and not currently running.
How to solve it:
- Download* Growl Version Detective
- Remove everything it identifies in the "Growl" tab. (Don't worry about the Frameworks tab)
- Trash /Applications/Growl.app
Voila. The App Store's "upgrade" button is replaced by "install". Smooth sailing from there. Including notifications that are top-rate. Hurrah.