This error typically appears when the Flash player is in use, preventing a new install. You should close all browsers or other applications that may be using Flash (which could be an Instant Messaging application for example), It will be worth looking at the Task Manager and close any Flash Player related processes (they have 'FlashPlayer' or 'FlashUtil' in the name).
make sure you have the correct processes closed. If flash dependent processes are NOT closed, then flash will not install/update PERIOD. I have tested this with the new offline installer and they MUST be closed.
Open a CMD prompt Run a Command as Administrator from the Windows 7 / Vista Run box
Copy/paste the following one by one or make a bat file to do it all in one step How to Write a Batch File (with Examples) - wikiHow
Ignore anything with a “::” at the beginning as that is just a remark
:: Kills any (known to me) programs that use flash player
taskkill.exe /im plugin-container.exe /f
taskkill.exe /im firefox.exe /f
taskkill.exe /im iexplore.exe /f
taskkill.exe /im flash* /f
taskkill.exe /im battle* /f
taskkill.exe /im Steam* /f
:: added July 7 2015 the weather channel app
taskkill.exe /im TWC.Win7.exe /f
That should close any flash dependent programs (that I know of)