Supondo que você esteja falando do aplicativo atual do Notificador do Google (há um aplicativo de terceiros chamado "Gmail Notifier"), provavelmente porque o Google abandonou o suporte para o Notificador do Google no final de janeiro de 2014.
Basicamente, eles sugerem que você use o navegador Chrome.
Do Google:
Google Notifier Beta is no longer supported. If you want to continue to receive notifications, you can use any of the following alternatives to Google Notifier Beta using the Chrome browser...
...Google thought the same thing, and today quietly discontinued the free tool, which has been around since 2005. Users looking to install the app are now being told by Google to simply install Chrome, which has desktop notifications built in...
Aviso enviado aos usuários pelo Google algumas semanas antes:
Important Announcement on Google Notifier Beta
We are writing to let you know about an important change to Google Notifier Beta. Starting on January 31, 2014, Google Notifier Beta will no longer be supported, meaning the app will no longer show recent emails and calendar events.
Since the Google Notifier Beta launched in 2005, a lot has changed. Smart phones can now notify us of new messages wherever we are, and improvements to web technology enable similar features to be built right into the browser.
If you want to continue to receive notifications, you can use any of the following alternatives to Google Notifier Beta using the Chrome browser:
To see the number of unread messages in your inbox at a glance, install the Gmail Checker Chrome app. To preview new messages on your desktop, go to Gmail's settings and enable Desktop Notifications. To get Calendar notifications on the desktop, go to Calendar's settings and enable Show floating desktop notifications. You can uninstall the Google Notifier Beta by following these instructions.
-- The Gmail and Calendar Teams