Hopefully Pat's suggestion gets you around this problem. We'd still like to get a better understanding of what's happening here.
Could you also please post the contents of the installer log?
It's located under /Users/<your_username/Logs/FlashPlayerInstallManager.log. You can attach it to a reply by clicking "Use Advanced Editor" in the reply window, then the Attach button at the bottom of the window, or any kind of file sharing link - dropbox, pastebin, etc. would work.
Thanks!
