I got that msg once. I subsequently realized there was another flash player icon window open, behind the screen I was working on. When I closed it, I didn’t get that msg again.
But, I STILL have been unable to install flash player on my OS X 10.9.3, after DAYS of trying to figure out what is preventing it.
Did you try to download the offline installer for Flash Player for MAC , as mentioned by Pat .
Did you get any error message.
You can also try to download Google Chrome, It has inbuilt flash player.
What error, if any, is being displayed when you attempt to install Flash Player?
Please post the contents of the /Users/<YourUserID>/Library/Logs/FlashPlayerInstallManager.log for the install attempts that are failing. These will be listed at the end of the file. Each attempt begins and ends with --- log start --- and --- log end ---.
Thank you in advance.