Want to clear programs that have been uninstalled from the Customize Notifications window?
To clear the Past Items list:

1. Use Regedit to navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\TrayNotify.

2. Delete the IconStreams Value Name.

3. Delete the PastIconsStream Value Name.

4. Close all instances of Windows Explorer.

5. Open Task Manager and select the Processes tab.

6. Select Explorer.exe and press End Process. This will close the shell.

7. In Task Manager, press File / New Task and type explorer.

8. Press OK.