If you are downloading via Safari, you must let the download complete before closing Safari and only then install
Has same problem... tried closing all Safari windows but it wouldn't work...
Realised that you have to "Quit Safari" instead of just closing all the safari windows... and the installer start to download again and ta-da... my adobe flash player is installed!
Hope this helps....
how do you "quit safari"?
From the very top left corner of your screen, choose Safari > Quit Safari
1. Click on apple icon in top left corner of screen.
2. Select Force Quit.
3. Close Safari