Trying to install updated Flash Player but after installing 51% message pops up saying quit Safari,

I downloaded and clicked the dmg to install latest update.  It got to 51% complete and then stopped instructing me to close Safari.  Sarfari was already closed and not running.  Hit retry and got same message.  Tried a reboot and install but still got same message.  Don't understand why it says close when it is already closed?