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In fact, you need to download it from the Adobe website > http://get.adobe.com/flashplayer Redownload Flash Player from that website and install it. Restart your Mac after finishing the installation.
If you get a message telling you that you cannot open the installer because it does not come from the Mac App Store, open System Preferences > Security & Privacy > General, press the padlock at the bottom left corner of the window, and choose "Anywhere" under "Allow applications downloaded from". See > http://support.apple.com/kb/HT5290?viewlocale=en_US&locale=en_US