Got this from apple discussions. Don't know if it will help or not.
Good luck
Dashboard is essentially a pared-down web browser. Adobe Flash installers usually look for open web browsers before installing and recommend they be shut down prior to install. So, try going into Dashboard and then move your mouse over any open widgets and then hold the option (or alt) key down and a small (x) should appear on the top left hand corner of the widget. Click that to close the widget. Repeat that for all the open widgets and then retry the Flash installer.
If you want to read it all
https://discussions.apple.com/thread...art=0&tstart=0