We encountered this problem when running SWF created with Flash CS6 on IE8. It will show a blank page with a smaller icon at the top left corner first. Then, a dialog box "Internet Explorer - Security Warning" shows up, Do you want to install this software? Name: Adobe Flash Player. with options "Install" and "Don't Install" click don't install will display the SWF right after. Install does not do much as it prompts the same message when you come back again.
The file works fine if running from Chrome. I didn't see this message using CS6 when I published the file last time (~ 3 months ago).
I tried a different way and it prompts: This content requires Flash player 11.7. We have no control over our users' player version and our users can't upgrade player on their own. What are the features in Flash CS6 requires 11.7 so that I can remove it?
If I saved it back to Flash CS5.5 then the message does not show up. What's in Flash CS6 that makes this happen. I didn't have this problem 3 months ago.